Strain sensing element, pressure sensor, microphone, blood pressure sensor, and touch panel

ABSTRACT

According to one embodiment, a strain sensing element is provided on a film unit configured to be deformed. The strain sensing element includes a functional layer, a first magnetic layer, a second magnetic layer, and a spacer layer. The functional layer includes at least one of an oxide and a nitride. The second magnetic layer is provided between the functional layer and the first magnetic layer. A magnetization of the second magnetic layer is variable in accordance with a deformation of the film unit. The spacer layer is provided between the first magnetic layer and the second magnetic layer. At least a part of the second magnetic layer is amorphous and includes boron.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 14/471,694,filed Aug. 28, 2014 and is based upon and claims the benefit of priorityfrom Japanese Patent Application No. 2013-196049, filed on Sep. 20,2013; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a strain sensingelement, a pressure sensor, a microphone, a blood pressure sensor, and atouch panel.

BACKGROUND

For pressure sensors using MEMS (micro electro mechanical systems)technology, there are a piezoresistance change type and an electrostaticcapacitance type, for example. On the other hand, a pressure sensorusing spin-electronics technology is proposed. In the pressure sensorusing spin-electronics technology, a resistance change in accordancewith strain is sensed. It is desired for strain sensing devices used forpressure sensors etc. to improve sensitivity, for example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 A and FIG. 1B are schematic views showing a strain sensingelement according to a first embodiment;

FIG. 2A to FIG. 2C are schematic views showing operations of the strainsensing element according to the first embodiment;

FIG. 3 is a schematic perspective view showing a strain sensing elementaccording to the first embodiment;

FIG. 4A and FIG. 4B are graphs showing characteristics of a strainsensing element;

FIG. 5A and FIG. 5B are graphs showing characteristics of a strainsensing element;

FIG. 6A and FIG. 6B are graphs showing characteristics of strain sensingelements;

FIG. 7A to FIG. 7D are microscope images showing characteristics of astrain sensing element;

FIG. 8A to FIG. 8D are microscope images showing characteristics of astrain sensing element;

FIG. 9A and FIG. 9B, are schematic diagrams showing characteristics ofstrain sensing elements;

FIG. 10A and FIG. 10B are schematic diagrams showing characteristics ofstrain sensing elements;

FIG. 11A and FIG. 11B are graphs showing characteristics of strainsensing elements;

FIG. 12A and FIG. 12B are graphs showing characteristics of strainsensing elements;

FIG. 13 is a schematic diagram showing characteristics of strain sensingelements;

FIG. 14 is a schematic diagram showing the strain sensing elementaccording to the first embodiment;

FIG. 15 is a microscope photographic image showing characteristics of astrain sensing element;

FIG. 16A and FIG. 16B are schematic diagrams showing characteristics ofthe strain sensing element;

FIG. 17A to FIG. 17E are schematic views showing other strain sensingelements according to the first embodiment;

FIG. 18A to FIG. 18C are schematic diagrams showing other strain sensingelements according to the first embodiment;

FIG. 19 is a schematic perspective view showing another strain sensingelement according to the first embodiment;

FIG. 20 is a schematic perspective view showing another strain sensingelement according to the first embodiment;

FIG. 21 is a schematic perspective view showing another strain sensingelement according to the first embodiment;

FIG. 22 is a schematic perspective view showing another strain sensingelement according to the first embodiment;

FIG. 23 is a schematic perspective view showing another strain sensingelement according to the first embodiment;

FIG. 24 is a schematic cross-sectional view showing a strain sensingelement according to a second embodiment;

FIG. 25A and FIG. 25B are schematic perspective views showing a pressuresensor according to a third embodiment;

FIG. 26A to FIG. 26C are schematic diagrams showing pressure sensorsaccording to the embodiment. The drawings show examples of theconnection state of a plurality of sensing elements;

FIG. 27A to FIG. 27E are schematic cross-sectional views in order of thesteps, showing a method for manufacturing a pressure sensor according tothe embodiment;

FIG. 28A to FIG. 28C are schematic diagrams showing a pressure sensoraccording to the embodiment;

FIG. 29A and FIG. 29B are schematic views showing a method formanufacturing a pressure sensor according to the embodiment;

FIG. 30A and FIG. 30B are schematic views showing a method formanufacturing a pressure sensor according to the embodiment;

FIG. 31A and FIG. 31B are schematic views showing a method formanufacturing a pressure sensor according to the embodiment;

FIG. 32A and FIG. 32B are schematic views showing a method formanufacturing a pressure sensor according to the embodiment;

FIG. 33A and FIG. 33B are schematic views showing a method formanufacturing a pressure sensor according to the embodiment;

FIG. 34A and FIG. 34B are schematic views showing a method formanufacturing a pressure sensor according to the embodiment;

FIG. 35A and FIG. 35B are schematic views showing a method formanufacturing a pressure sensor according to the embodiment;

FIG. 36A and FIG. 36B are schematic views showing a method formanufacturing a pressure sensor according to the embodiment;

FIG. 37A and FIG. 37B are schematic views showing a method formanufacturing a pressure sensor according to the embodiment;

FIG. 38A and FIG. 38B are schematic views showing a method formanufacturing a pressure sensor according to the embodiment;

FIG. 39A and FIG. 39B are schematic views showing a method formanufacturing a pressure sensor according to the embodiment;

FIG. 40A and FIG. 40B are schematic views showing a method formanufacturing a pressure sensor according to the embodiment;

FIG. 41 is a schematic cross-sectional view showing a microphoneaccording to a fourth embodiment;

FIG. 42A and FIG. 42B are schematic views showing a blood pressuresensor according to a fifth embodiment; and

FIG. 43 is a schematic diagram showing a touch panel according to asixth embodiment.

DETAILED DESCRIPTION

According to one embodiment, a strain sensing element is provided on afilm unit configured to be deformed. The strain sensing element includesa functional layer, a first magnetic layer, a second magnetic layer, anda spacer layer. The functional layer includes at least one of an oxideand a nitride. The second magnetic layer is provided between thefunctional layer and the first magnetic layer. A magnetization of thesecond magnetic layer is variable in accordance with a deformation ofthe film unit. The spacer layer is provided between the first magneticlayer and the second magnetic layer. At least a part of the secondmagnetic layer is amorphous and includes boron.

According to one embodiment, a pressure sensor includes a strain sensingelement and a film unit. The strain sensing element is provided on thefilm unit configured to be deformed. The strain sensing element includesa functional layer including at least one of an oxide and a nitride, afirst magnetic layer, a second magnetic layer provided between thefunctional layer and the first magnetic layer, a magnetization of thesecond magnetic layer being variable in accordance with a deformation ofthe film unit, and a spacer layer provided between the first magneticlayer and the second magnetic layer. At least a part of the secondmagnetic layer is amorphous and includes boron.

According to one embodiment, a microphone comprising a pressure sensor.The pressure sensor includes a strain sensing element and a film unit.The strain sensing element is provided on the film unit configured to bedeformed. The strain sensing element includes a functional layerincluding at least one of an oxide and a nitride, a first magneticlayer, a second magnetic layer provided between the functional layer andthe first magnetic layer, a magnetization of the second magnetic layerbeing variable in accordance with a deformation of the film unit, and aspacer layer provided between the first magnetic layer and the secondmagnetic layer. At least a part of the second magnetic layer isamorphous and includes boron.

According to one embodiment, a blood pressure sensor includes a pressuresensor. The pressure sensor includes a strain sensing element and a filmunit. The strain sensing element is provided on the film unit configuredto be deformed. The strain sensing element includes a functional layerincluding at least one of an oxide and a nitride, a first magneticlayer, a second magnetic layer provided between the functional layer andthe first magnetic layer, a magnetization of the second magnetic layerbeing variable in accordance with a deformation of the film unit, and aspacer layer provided between the first magnetic layer and the secondmagnetic layer. At least a part of the second magnetic layer isamorphous and includes boron.

According to one embodiment, a touch panel includes a pressure sensor.The pressure sensor includes a strain sensing element and a film unit.The strain sensing element is provided on the film unit configured to bedeformed. The strain sensing element includes a functional layerincluding at least one of an oxide and a nitride, a first magneticlayer, a second magnetic layer provided between the functional layer andthe first magnetic layer, a magnetization of the second magnetic layerbeing variable in accordance with a deformation of the film unit, and aspacer layer provided between the first magnetic layer and the secondmagnetic layer. At least a part of the second magnetic layer isamorphous and includes boron.

Various embodiments will be described hereinafter with reference to theaccompanying drawings.

The drawings are schematic or conceptual; and the relationships betweenthe thickness and width of portions, the proportions of sizes amongportions, etc. are not necessarily the same as the actual valuesthereof. Further, the dimensions and proportions may be illustrateddifferently among drawings, even for identical portions.

In the specification of this application and the drawings, componentssimilar to those described in regard to a drawing thereinabove aremarked with the same reference numerals, and a detailed description isomitted as appropriate.

First Embodiment

FIG. 1A and FIG. 1B are schematic views illustrating a strain sensingelement according to a first embodiment.

FIG. 1A is a schematic perspective view of the strain sensing element,and FIG. 1B is a schematic cross-sectional view illustrating a pressuresensor in which the strain sensing element is used.

As shown in FIG. 1A, a strain sensing element 50 according to theembodiment includes a functional layer 25, a first magnetic layer 10, asecond magnetic layer 20, and a spacer layer 30.

For the functional layer 25, at least one of an oxide and a nitride isused, for example. The functional layer 25 includes at least one of anoxide of at least one selected from a first group consisting ofmagnesium (Mg), aluminum (Al), silicon (Si), titanium (Ti), vanadium(V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni),copper (Cu), zinc (Zn), zirconium (Zr), niobium (Nb), molybdenum (Mo),ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), hafnium (Hf),tantalum (Ta), tungsten (W), tin (Sn), cadmium (Cd), and gallium (Ga)and a nitride of at least one selected from the first group, forexample.

The functional layer 25 may include an oxide of at least one selectedfrom a second group consisting of magnesium, titanium, vanadium, zinc,tin, cadmium, and gallium, for example. Magnesium oxide is used for thefunctional layer 25, for example.

The second magnetic layer 20 is provided between the functional layer 25and the first magnetic layer 10. The second magnetic layer 20 includesan amorphous portion. The second magnetic layer 20 includes boron (B).The magnetization of the second magnetic layer 20 (the directionthereof) is variable. The magnetization of the second magnetic layer 20changes in accordance with the strain applied to the second magneticlayer 20. The second magnetic layer 20 has an amorphous structure, forexample. As described later, the second magnetic layer 20 may include anamorphous portion and a crystalline portion. That is, at least part ofthe second magnetic layer 20 is amorphous.

The spacer layer 30 is provided between the first magnetic layer 10 andthe second magnetic layer 20.

The second magnetic layer 20 is a magnetization free layer, for example.The first magnetic layer 10 is a reference layer, for example. Amagnetization pinned layer or a magnetization free layer is used as thereference layer. The change in magnetization of the second magneticlayer 20 is easier than the change in magnetization of the firstmagnetic layer 10, for example. When a stress is applied to the strainsensing element 50 and the strain sensing element 50 is provided with astrain, the relative angle between the magnetization of the firstmagnetic layer 10 and the magnetization of the second magnetic layer 10is changed.

The direction from the first magnetic layer 10 toward the secondmagnetic layer 20 is defined as the Z-axis direction (the stackingdirection), for example. One direction perpendicular to the Z-axisdirection is defined as the X-axis direction. The directionperpendicular to the Z-axis direction and the X-axis direction isdefined as the Y-axis direction.

In this example, a first electrode E1 and a second electrode E2 arefurther provided. The first magnetic layer 10 is provided between thefirst electrode E1 and the second electrode E2. The spacer layer 30 isprovided between the first magnetic layer 10 and the second electrodeE2. The second magnetic layer 20 is provided between the spacer layer 30and the second electrode E2. The functional layer 25 is provided betweenthe second magnetic layer 20 and the second electrode E2. In thisexample, the second magnetic layer 20 is in contact with the functionallayer 25.

By applying a voltage between the first electrode E1 and the secondelectrode E2, a current can be passed through a stacked body 10 sincluding the first magnetic layer 10, the spacer layer 30, the secondmagnetic layer 20, and the functional layer 25. The current runs alongthe Z-axis direction between the first magnetic layer 10 and the secondmagnetic layer 20, for example.

As shown in FIG. 2B, the strain sensing element 50 is used for apressure sensor 110. The pressure sensor 110 includes a film unit 70 andthe strain sensing element 50. The film unit 70 has a flexible region.The film unit 70 can be deformed. The strain sensing element 50 is fixedto the film unit 70. In the specification of this application, the stateof being fixed includes the state of being directly fixed and the stateof being indirectly fixed by another component. The state where thesensing element 50 is fixed to the film unit 70 includes a state wherethe relative positions between the sensing element 50 and the film unit70 are fixed, for example. The strain sensing element 50 is provided onpart of the film unit 70, for example.

In the specification of this application, the state of being “providedon” includes not only the state of being provided in direct contact butalso the state of being provided via another component.

When a force 79 is applied to the film unit 70, the film unit 70 isdeformed. A strain is generated in the strain sensing element 50 inconjunction with the deformation. The magnetization of the secondmagnetic layer 20 changes in accordance with the deformation of the filmunit, for example.

In the strain sensing element 50 according to the embodiment, a strainis generated in the strain sensing element 50 when the film unit 70 isdeformed by a force from the outside, for example. The strain sensingelement 50 converts the change in strain to a change in electricresistance.

The operation in which the strain sensing element 50 functions as astrain sensor is based on application of “inverse magnetostrictioneffect” and “magnetoresistance effect.” The “inverse magnetostrictioneffect” is obtained in a ferromagnetic layer used as a magnetizationfree layer. The “magnetoresistance effect” is exhibited in a stackedfilm of a magnetization free layer, a spacer layer, and a referencelayer (for example, a magnetization pinned layer).

The “inverse magnetostriction effect” is a phenomenon in which themagnetization of a ferromagnetic material is changed by a straingenerated in the ferromagnetic material. That is, when an externalstrain is applied to the stacked body 10 s of the strain sensing element50, the magnetization direction of the magnetization free layer ischanged. Consequently, the relative angle between the magnetization ofthe magnetization free layer and the magnetization of the referencelayer (for example, a magnetization pinned layer) is changed. At thistime, a change in electric resistance is caused by the“magnetoresistance effect (MR effect).” The MR effect includes GMR(giant magnetoresistance) effect, TMR (tunneling magnetoresistance)effect, or the like, for example. The MR effect is exhibited by passinga current through the stacked body 10 s to read the change in relativeangle between the directions of the magnetizations as an electricresistance change. A strain is generated in the stacked body 10 s (thestrain sensing element 50), the direction of the magnetization of themagnetization free layer is changed by the strain, and the relativeangle between the direction of the magnetization of the magnetizationfree layer and the direction of the magnetization of the reference layer(for example, a magnetization pinned layer) is changed, for example.That is, the MR effect appears due to the inverse magnetostrictioneffect.

When the ferromagnetic material used for the magnetization free layerhas a positive magnetostriction constant, the direction of themagnetization changes so that the angle between the direction of themagnetization and the direction of a tensile strain becomes smaller andthe angle between the direction of the magnetization and the directionof a compressive strain becomes larger. When the ferromagnetic materialused for the magnetization free layer has a negative magnetostrictionconstant, the direction of the magnetization changes so that the anglebetween the direction of the magnetization and the direction of atensile strain becomes larger and the angle between the direction of themagnetization and the direction of a compressive strain becomes smaller.

When the combination of the materials of the stacked body of themagnetization free layer, the spacer layer, and the reference layer (forexample, a magnetization pinned layer) has a positive magnetoresistanceeffect, the electric resistance decreases as the relative angle betweenthe magnetization free layer and the magnetization pinned layerdecreases. When the combination of the materials of the stacked body ofthe magnetization free layer, the spacer layer, and the magnetizationpinned layer has a negative magnetoresistance effect, the electricresistance increases as the relative angle between the magnetizationfree layer and the magnetization pinned layer decreases.

Examples of the change in magnetization will now be described using anexample in which the ferromagnetic materials used for the magnetizationfree layer has a positive magnetostriction constant, and the stackedbody including the magnetization free layer, the spacer layer, and thereference layer (for example, a magnetization pinned layer) has apositive magnetoresistance effect.

FIG. 2A to FIG. 2C are schematic views illustrating operations of thestrain sensing element according to the first embodiment.

FIG. 2A corresponds to a state where a tensile stress is is applied tothe strain sensing element 50 (a tensile state STt). FIG. 2B correspondsto a state where the strain sensing element 50 has no strain (ano-strain state ST0). FIG. 2C corresponds to a state where a compressivestress cs is applied to the strain sensing element 50 (a compressivestate STc).

In the drawings, for easier viewing of the drawings, the first magneticlayer 10, the second magnetic layer 20, and the spacer layer 30 aredepicted, and the functional layer 25 is omitted. In this example, thesecond magnetic layer 20 is a magnetization free layer, and the firstmagnetic layer 10 is a magnetization pinned layer.

As shown in FIG. 2B, in the no-strain state ST0 where there is no strain(for example, the initial state), the relative angle between themagnetization 20 m of the second magnetic layer 20 and the magnetization10 m of the first magnetic layer 10 (for example, a magnetization pinnedlayer) is set to a prescribed value. The direction of the magnetizationof the magnetic layer in the initial state is set by a hard bias, theshape anisotropy of the magnetic layer, or others, for example. In thisexample, the magnetization 20 m of the second magnetic layer 20 (amagnetization free layer) and the magnetization 10 m of the firstmagnetic layer 10 (for example, a magnetization pinned layer) cross eachother.

As shown in FIG. 2A, in the tensile state STt, when a tensile stress tsis applied, a strain in accordance with the tensile stress ts isgenerated in the strain sensing element 50. At this time, themagnetization 20 m of the second magnetic layer 20 (a magnetization freelayer) changes from the no-strain state ST0 so that the angle betweenthe magnetization 20 m and the direction of the tensile stress tsbecomes smaller. In the example shown in FIG. 2A, when a tensile stressts is applied, the relative angle between the magnetization 20 m of thesecond magnetic layer 20 (a magnetization free layer) and themagnetization 10 m of the first magnetic layer 10 (for example, amagnetization pinned layer) is decreased as compared to the no-strainstate ST0. Thereby, the electric resistance in the strain sensingelement 50 is decreased as compared to the electric resistance in theno-strain state ST0.

As shown in FIG. 2C, in the compressive state STc, when a compressivestress cs is applied, the magnetization 20 m of the second magneticlayer 20 (a magnetization free layer) changes from the no-strain stateST0 so that the angle between the magnetization 20 m and the directionof the compressive stress cs becomes larger. In the example shown inFIG. 2C, when a compressive stress cs is applied, the relative anglebetween the magnetization 20 m of the second magnetic layer 20 (amagnetization free layer) and the magnetization 10 m of the firstmagnetic layer 10 (for example, a magnetization pinned layer) isincreased as compared to the no-strain state ST0. Thereby, the electricresistance in the strain sensing element 50 is increased.

Thus, in the strain sensing element 50, the change in strain generatedin the strain sensing element 50 is converted to a change in electricresistance. In the operations mentioned above, the amount of change inelectric resistance (dR/R) per unit strain (dε) is referred to as agauge factor (GF). By using a strain sensing element with a high gaugefactor, a high-sensitivity strain sensor is obtained.

Examples of the strain sensing element 50 will now be described.

In the following, the description of “material A/material B” refers tothe state where a layer of material B is provided on a layer of materialA.

FIG. 3 is a schematic perspective view illustrating a strain sensingelement according to the first embodiment.

As shown in FIG. 3, a strain sensing element 51 used in the embodimentincludes the first electrode E1, an underlayer 10 l, a pinning layer 10p, the first magnetic layer 10, the spacer layer 30, the second magneticlayer 20, the functional layer 25, and a cap layer 26 c. The underlayer10 l is provided between the first electrode E1 and the first magneticlayer 10. The pinning layer 10 p is provided between the underlayer 10 land the first magnetic layer 10. The cap layer 26 c is provided betweenthe second magnetic layer 20 and the second electrode E2. In thisexample, the first magnetic layer 10 includes a first magnetizationpinned layer 10 a, a second magnetization pinned layer 10 b, and amagnetic coupling layer 10 c. The first magnetization pinned layer 10 ais provided between the second magnetization pinned layer 10 b and thespacer layer 30. The magnetic coupling layer 10 c is provided betweenthe second magnetization pinned layer 10 b and the first magnetizationpinned layer 10 a.

As the underlayer 10 l, Ta/Ru is used, for example. The thickness (thelength in the Z-axis direction) of the Ta layer is 3 nanometers (nm),for example. The thickness of the Ru layer is 2 nm, for example.

As the pinning layer 10 p, an IrMn layer with a thickness of 7 nm isused, for example.

As the second magnetization pinned layer 10 b, a Co₇₅Fe₂₅ layer with athickness of 2.5 nm is used, for example.

As the magnetic coupling layer 10 c, a Ru layer with a thickness of 0.9nm is used, for example.

As the first magnetization pinned layer 10 a, a Co₄₀Fe₄₀B₂₀ layer with athickness of 3 nm is used, for example.

As the spacer layer 30, a Mg—O layer with a thickness of 1.6 nm is used,for example.

As the second magnetic layer 20, Co₄₀Fe₄₀B₂₀ with a thickness of 4 nm isused, for example.

As the functional layer 25, a Mg—O layer with a thickness of 1.5 nm isused, for example.

As the cap layer 26 c, Ta/Ru is used, for example. The thickness of theTa layer is 1 nm, for example. The thickness of the Ru layer is 5 nm,for example.

As the first electrode E1 and the second electrode E2, a metal is used,for example.

Characteristics of the strain sensing element according to theembodiment will now be described.

The material and thickness of the layers included in a first sample S01are as follows:

The underlayer 10 l: Ta (1 nm)/Ru (2 nm)

The pinning layer 10 p: Ir₂₂Mn₇₈ (7 nm)

The second magnetization pinned layer 10 b: Co₇₅Fe₂₅ (2.5 nm)

The magnetic coupling layer 10 c: Ru (0.9 nm)

The first magnetization pinned layer 10 a: Co₄₀Fe₄₀B₂₀ (3 nm)

The spacer layer 30: Mg—O (1.6 nm)

The second magnetic layer 20: Co₄₀Fe₄₀B₂₀ (4 nm)

The functional layer 25: Mg—O (1.5 nm)

The cap layer 26 c: Cu (1 nm)/Ta (20 nm)/Ru (50 nm)

On the other hand, in a second sample S02, the functional layer 25 isnot provided. Otherwise, the configuration of the second sample S02 isthe same as the first sample S01.

As mentioned above, in the first sample S01, a Co₄₀Fe₄₀B₂₀ layer with athickness of 4 nm is used as the second magnetic layer 20. A Mg—O layerwith a thickness of 1.5 nm is used as the functional layer 25. On theother hand, in the second sample S02, the functional layer 25 is notprovided.

The Mg—O layers used as the spacer layer 30 and the functional layer 25are formed by forming a Mg layer with a thickness of 1.6 nm and thenperforming surface oxidation using IAO (ion beam-assisted oxidation)processing. The oxidation conditions in the fabrication of the Mg—Olayer for the functional layer 25 are weaker than the oxidationconditions in the fabrication of the Mg—O layer for the spacer layer 30,for example. The resistance-area product (RA) of the Mg—O layer for thefunctional layer 25 is lower than the resistance-area product (RA) ofthe Mg—O layer for the spacer layer 30. When the resistance-area product(RA) of the Mg—O layer for the functional layer 25 is higher than theresistance-area product (RA) of the Mg—O layer for the spacer layer 30,the parasitic resistance is increased due to the functional layer 25,the MR ratio is reduced, and the gauge factor is decreased. By settingthe resistance-area product (RA) of the Mg—O layer for the functionallayer 25 lower than the resistance-area product (RA) of the Mg—O layerfor the spacer layer 30, the parasitic resistance can be reduced, a highMR ratio is obtained, and a high gauge factor is obtained.

The stacked film mentioned above is formed on the first electrode E1,and the second electrode E2 is formed on the stacked film. The stackedfilm mentioned above (the first sample S01 and the second sample S02) isprocessed into a dot-like element. The element size of the stacked film(sample) is 20 μm×20 μm. The vertical current passage characteristicsbetween the first electrode E1 and the second electrode E2 areinvestigated.

The strain sensor characteristics of the samples mentioned above areinvestigated by the substrate bending method. In this method, asubstrate (wafer) on which the sample is formed is cut into arectangular shape, and the four point bending method with knife edges isused to apply a stress to the wafer to form a strain in the wafer. Aload cell is incorporated in the knife edge that bends the rectangularwafer. The strain applied to the sample (the strain sensing element) onthe wafer is found by the load measured by the load cell.

Formula 1 below regarding two side support beams is used for thecalculation of the strain.ε=−3(L ₁ −L ₂)G/(2Wt ² e _(s))  Formula 1

In Formula 1 above, “e_(s)” is the Young's modulus of the wafer. “L₁” isthe inter-edge length of the outer knife edges. “L₂” is the inter-edgelength of the inner knife edges. “W” is the width of the rectangularwafer. “t” is the thickness of the rectangular wafer. “G” is the loadapplied to the knife edge. The load applied to the knife edge can bealtered continuously by motor control.

FIG. 4A and FIG. 4B are graphs illustrating characteristics of a strainsensing element.

FIG. 5A and FIG. 5B are graphs illustrating characteristics of a strainsensing element.

FIG. 4A and FIG. 4B show the investigation results of the strain sensorcharacteristics of the first sample S01. FIG. 4A shows the measurementresults of the magnetic field dependence of the electric resistance whenthe strain ε is 0.8×10⁻³, 0.6×10⁻³, 0.4×10⁻³, 0.2×10⁻³, and 0.0×10⁻³.FIG. 4B shows the measurement results of the magnetic field dependenceof the electric resistance when the strain ε is −0.2×10⁻³, −0.4×10⁻³,−0.6×10⁻³, and −0.8×10⁻³.

FIG. 5A and FIG. 5B show the investigation results of the strain sensorcharacteristics of the second sample S02. FIG. 5A shows the measurementresults of the magnetic field dependence of the electric resistance whenthe strain ε is 0.8×10⁻³, 0.6×10⁻³, 0.4×10⁻³, 0.2×10⁻³, and 0.0×10⁻³.FIG. 5B shows the measurement results of the magnetic field dependenceof the electric resistance when the strain ε is −0.2×10⁻³, −0.4×10⁻³,−0.6×10⁻³, and −0.8×10⁻³.

The horizontal axis of the drawings is the external magnetic field H(oersteds; Oe). The vertical axis is the electric resistance R (ohm; Ω).The direction of the external magnetic field H in the measurement is adirection parallel to the plane of the first magnetization pinned layer10 a. The negative external magnetic field H corresponds to the magneticfield in the same direction as the direction of the magnetization of thefirst magnetization pinned layer 10 a.

The direction of the application of strain ε is a directionperpendicular to the magnetization direction of the first magnetic layer(for example, a magnetization pinned layer) in the X-Y plane. In thespecification of this application, the value of the strain ε beingpositive corresponds to tensile strain. The value of the strain ε beingnegative corresponds to compressive strain.

As can be seen from FIG. 4A, FIG. 4B, FIG. 5A, and FIG. 5I, the R-H loopshape changes with the value of the strain ε in the first sample S01 andthe second sample S02. This indicates that the in-plane magneticanisotropy of the second magnetic layer 20 (a magnetization free layer)changes due to the inverse magnetostriction effect.

FIG. 6A and FIG. 6B are graphs illustrating characteristics of strainsensing elements.

FIG. 6A corresponds to the first sample S01, and FIG. 6B corresponds tothe second sample S02. The drawings show the change in electricresistance R when the external magnetic field H is fixed and the strainε is changed continuously in a range between −0.8×10⁻³ and 0.8×10⁻³. Thehorizontal axis of the drawings is the strain ε, and the vertical axisis the electric resistance R. The change in strain ε is both the changefrom −0.8×10⁻³ toward 0.8×10⁻³ and the change from 0.8×10⁻³ toward−0.8×10⁻³. The results show strain sensor characteristics. The gaugefactor is calculated from the drawings.

The gauge factor GF is expressed by GF=(dR/R)/dε.

From FIG. 6A, the gauge factor in the first sample S01 is calculated tobe 4027. From FIG. 6B, the gauge factor in the second sample S02 iscalculated to be 895.

Thus, in the case where the same second magnetic layer 20 (amagnetization free layer of a Co₄₀Fe₄₀B₂₀ layer with a thickness of 4nm) is used, the gauge factor can be significantly improved by using aMg—O layer with a thickness of 1.5 nm as the functional layer 25.

On the other hand, the MR ratio of the first sample S01 is 149%. The MRratio of the second sample S02 is 188%. The coercivity Hc of the firstsample S01 is 3.2 Oe. The coercivity Hc of the second sample S02 is 27Oe. The magnetostriction constant λ of the first sample S01 is 20 ppm.The magnetostriction constant λ of the second sample S02 is 30 ppm.

Such a difference in gauge factor dependent on the presence or absenceof the functional layer 25 is presumed to be due to the fact that thecoercivity Hc of the Co₄₀Fe₄₀B₂₀ layer that is the second magnetic layer20 (a magnetization free layer) is different.

As mentioned above, the coercivity Hc of the second sample S02 is 27 Oe,whereas the coercivity Hc of the first sample S01 is 3.2 Oe. Thecoercivity Hc of the first sample S01 is very small. The improvement ingauge factor due to the decrease in coercivity Hc can be explained asfollows.

As described in regard to FIG. 2A to FIG. 2C, when a strain is generatedin a magnetization free layer (the second magnetic layer 20), themagnetization direction of the magnetization free layer changes due tothe inverse magnetostriction effect. At this time, by using a magneticmaterial with a large magnetostriction constant λ as the magnetizationfree layer, the force of rotating magnetization works greatly withrespect to the strain; therefore, the gauge factor can be improved. Onthe other hand, the gauge factor depends also on the coercivity of themagnetization free layer. The coercivity is a physical parameterreflecting the ease of magnetization rotation of the magnetization freelayer. Materials with a large coercivity have a strong force of keepingthe magnetization direction as it is. Therefore, in materials with alarge coercivity, a change in magnetization direction due to the inversemagnetostriction effect is less likely to occur.

Thus, a high gauge factor is obtained when the magnetostriction constantλ is large in the magnetization free layer. A high gauge factor isobtained when the coercivity in the magnetization free layer is small.

As mentioned above, the value of the magnetostriction constant λ in thefirst sample S01 is relatively close to that in the second sample S02,and is sufficiently large. On the other hand, the coercivity Hc in thefirst sample S01 is significantly smaller than that in the second sampleS02, and is approximately 1/10 of that. In the first sample S01, it ispresumed that the effect of the reduction in coercivity Hc greatlycontributes to the increase in gauge factor.

The small coercivity Hc and the large magnetostriction constant λobtained in the first sample S01 are obtained by providing the Mg—Olayer as the functional layer 25 on the second magnetic layer 20 (amagnetization free layer) of a Co₄₀Fe₄₀B₂₀ layer.

An investigation by the inventors of this application has revealed thatthe crystal structure of the Co₄₀Fe₄₀B₂₀ layer of the second magneticlayer 20 (a magnetization free layer) changes with the presence orabsence of the functional layer 25. It has been found that thedifference in crystal structure of Co₄₀Fe₄₀B₂₀ has relation to thedifference in coercivity Hc. The difference in crystal structure willnow be described.

FIG. 7A to FIG. 7D are microscope images illustrating characteristics ofa strain sensing element.

FIG. 7A is a cross-sectional transmission electron microscope(cross-sectional TEM) photographic image of the strain sensing elementof the first sample S01. FIG. 7A is a photograph of the stackedstructure of the first sample S01.

FIG. 7B to FIG. 7D are crystal lattice diffraction images obtained bynanodiffraction of an electron beam of points P1 to P3 of FIG. 7A,respectively.

FIG. 7A shows a region including a part of the second magnetizationpinned layer 10 b (a Co₅₀Fe₅₀ layer) to a part of the cap layer 26 c (aRu layer).

As can be seen from FIG. 7A, the first magnetization pinned layer 10 a(a Co—Fe—B layer) includes a crystal portion. Also the spacer layer 30(a Mg—O layer) is a crystal. On the other hand, in the most part of thesecond magnetic layer 20 (a Co—Fe—B layer that is a magnetization freelayer) sandwiched by the spacer layer 30 and the functional layer 25 (aMg—O layer), a regular atomic arrangement is not observed. That is, thesecond magnetic layer 20 is amorphous.

The crystal state can be checked by a crystal lattice diffraction image.The crystal lattice diffraction images of points P1 to P3 in FIG. 7A areshown in FIG. 7B to FIG. 7D, respectively. Point P1 corresponds to thefirst magnetization pinned layer 10 a. Point P2 corresponds to thespacer layer 30. Point P3 corresponds to the second magnetic layer 20 (amagnetization free layer).

As shown in FIG. 7B, diffraction spots are observed in the diffractionimage of point P1 corresponding to the first magnetization pinned layer10 a (a Co—Fe—B layer). The diffraction spots are due to the fact thatthe first magnetization pinned layer 10 a has a crystal structure.

As shown in FIG. 7C, diffraction spots are observed in the diffractionimage of point P2 corresponding to the spacer layer 30 (a Mg—O layer).The diffraction spots are due to the fact that the spacer layer 30 has acrystal structure.

On the other hand, as shown in FIG. 7D, distinct diffraction spots arenot observed in the diffraction image of point P3 corresponding to thesecond magnetic layer 20 (a Co—Fe—B layer of a magnetization freelayer). In the diffraction image, a ring-like diffraction imagereflecting an amorphous structure is observed. The result shows that thesecond magnetic layer 20 (a Co—Fe—B layer of a magnetization free layer)of the first sample S01 includes an amorphous portion.

FIG. 8A to FIG. 8D are microscope images illustrating characteristics ofa strain sensing element.

FIG. 8A is a cross-sectional transmission electron microscope(cross-sectional TEM) photographic image of the strain sensing elementof the second sample S02. FIG. 8B to FIG. 8D are crystal latticediffraction images obtained by nanodiffraction of an electron beam ofpoints P4 to P6 of FIG. 8A, respectively.

As can be seen from FIG. 8A, the first magnetization pinned layer 10 a(a Co—Fe—B layer) includes a crystal portion, and also the spacer layer30 (a Mg—O layer) is a crystal. Also the second magnetic layer 20 (aCo—Fe—B layer that is a magnetization free layer) on the spacer layer 30includes a large amount of crystal portions.

As shown in FIG. 8B, diffraction spots due to a crystal structure arefound in the diffraction image of the first magnetization pinned layer10 a (a Co—Fe—B layer).

As shown in FIG. 8C, diffraction spots due to a crystal structure arefound in the diffraction image of the spacer layer 30 (a Mg—O layer).

As shown in FIG. 8D, diffraction spots due to a crystal structure arefound also in the diffraction image of the second magnetic layer 20 (aCo—Fe—B layer of a magnetization free layer). The result shows that themost part of the second magnetic layer 20 (a Co—Fe—B layer of amagnetization free layer) of the second sample S02 has a crystalstructure.

As can be seen from FIG. 7A to FIG. 7D, the magnetization free layer ofthe first sample S01 showing a high gauge factor includes an amorphousstructure. On the other hand, as can be seen from FIG. 8A to FIG. 8D,the magnetization free layer of the second sample S02 that has showed alow gauge factor has a crystal structure.

As described above, in each of the first sample S01 and the secondsample S02, a Co₄₀Fe₄₀B₂₀ layer (4 nm) of the same composition is usedas the magnetization free layer. In spite of this, the first sample S01and the second sample S02 have different gauge factors and differentcrystal states. It is presumed that this reflects the presence orabsence of the functional layer 25 provided on the magnetization freelayer (a Co₄₀Fe₄₀B₂₀ layer (4 nm)).

The difference between the crystal states of the magnetization freelayers of the first sample S01 and the second sample S02 is furtherdescribed.

FIG. 9A, FIG. 9B, FIG. 10A, and FIG. 10B are schematic diagramsillustrating characteristics of strain sensing elements.

FIG. 9B corresponds to part of FIG. 7A, and FIG. 10B corresponds to partof FIG. 8A.

FIG. 9A and FIG. 10A are the investigation results of the depth profileof elements of the samples obtained by electron energy-loss spectroscopy(EELS). FIG. 9A corresponds to the sample S01, and shows the depthprofile of elements on line L1 shown in FIG. 7A. FIG. 10B corresponds tothe second sample S02, and shows the depth profile of elements on lineL2 shown in FIG. 8A. In these drawings, the horizontal axis is theintensity Int (an arbitrary unit) of detection of elements. The verticalaxis is the depth Dp (nm). The depth Dp corresponds to the distance inthe Z-axis direction, for example. These drawings show depth profilesregarding iron, boron, and oxygen.

As shown in FIG. 10A, in the second sample S02, the intensity Int ofboron in the cap layer 26 c is higher than the intensity Int of boron inthe second magnetic layer 20 (a Co—Fe—B layer that is a magnetizationfree layer). In the second magnetic layer 20, the intensity Int of boronin a portion on the cap layer 26 c side is higher than the intensity Intof boron in a central portion of the second magnetic layer 20. It ispresumed that boron is diffused from the second magnetic layer 20 to thecap layer 26 c side, and the concentration of boron in the secondmagnetic layer 20 is reduced.

On the other hand, as shown in FIG. 9A, in the first sample S01, a peakof boron appears in a central portion of the second magnetic layer 20 (aCo—Fe—B layer of a magnetization free layer). The boron content of thecap layer 26 c is small. The boron concentration of the second magneticlayer 20 (a Co—Fe—B layer of a magnetization free layer) is hardlydiffused to other layers, and maintains the initial state at the time offilm formation.

From the foregoing, it is presumed that the functional layer (in thisexample, a Mg—O layer) provided on the second magnetic layer 20 (amagnetization free layer) has the effect of a diffusion barrier thatsuppresses the diffusion of boron from the second magnetic layer 20.

The above results suggest that the crystallization in the Co₄₀Fe₄₀B₂₀layer of the second sample S02 in which the functional layer 25 is notprovided proceeds more than that in the Co₄₀Fe₄₀B₂₀ layer of the firstsample S01. That is, in the first sample S01, the Co₄₀Fe₄₀B₂₀ layermaintains the amorphous structure. On the other hand, crystallizationhas proceeded in the second sample S02 in which the functional layer 25is not provided. The cause that crystallization is progressed in thesecond sample S02 is probably that boron of the magnetization free layeris diffused and the boron content of the magnetization free layer isreduced.

FIG. 11A and FIG. 11B are graphs illustrating characteristics of strainsensing elements.

The drawings show the investigation results of X-ray diffraction ofCo₄₀Fe₄₀B₂₀ layers. FIG. 11A and FIG. 11B correspond to the first sampleS01 and the second sample S02, respectively. The horizontal axis of thedrawings is the rotation angle 2θ (degrees). The vertical axis is theintensity Int.

It is difficult to obtain diffraction peaks of only the Co₄₀Fe₄₀B₂₀layer in the sample in X-ray diffraction. Hence, the following modelfilms are used in these samples. Sample Sr1 shown in FIG. 11A has astacked structure of a first Mg—O layer (the spacer layer 30)/aCo₄₀Fe₄₀B₂₀ layer/a second Mg—O (the functional layer 25)/Ta(corresponding to the cap layer 26 c). Sample Sr1 has the functionallayer 25, and corresponds to the first sample S01. On the other hand,sample Sr2 shown in FIG. 11B has a stacked structure of a first Mg—Olayer (the spacer layer 30)/a Co₄₀Fe₄₀B₂₀ layer/Ta (corresponding to thecap layer 26 c). Sample Sr2 does not have the functional layer 25, andcorresponds to the second sample S02.

In FIG. 11A and FIG. 11B, X-ray diffraction results after annealing of320° C. and 1 H and before the annealing are shown for reference.

As can be seen from FIG. 11A and FIG. 11B, it is found that beforeannealing, no X-ray diffraction peak is found in either sample Sr1 orsample Sr2, and the magnetization free layers of both sample Sr1 andsample Sr2 are amorphous. On the other hand, after annealing, adiffraction peak of Co₅₀Fe₅₀ appears in sample Sr2 more strongly than insample Sr1.

This means that the crystallization in the Co₄₀Fe₄₀B₂₀ layer of thesecond sample S02 in which the functional layer 25 is not provided hasproceeded more than that in the Co₄₀Fe₄₀B₂₀ layer of the first sampleS01. That is, in the first sample S01, the Co₄₀Fe₄₀B₂₀ layer maintainsthe amorphous structure even after annealing. On the other hand, in thesecond sample S02 in which the functional layer 25 is not provided,crystallization proceeds after annealing.

FIG. 12A and FIG. 12B are graphs illustrating characteristics of strainsensing elements.

The drawings show characteristics of the first sample S01 and the secondsample S02 mentioned above and a third sample S03. In the third sampleS03, Fe₅₀Co₅₀ (thickness: 4 nm) including no boron is used as themagnetization free layer. The third sample S03 has the sameconfiguration as the second sample S02 except for the magnetization freelayer.

FIG. 12A shows the coercivity (Oe). FIG. 12B shows the magnetostrictionconstant λ (ppm). For the first sample S01 and the second sample S02,values of before annealing (BA) and values after annealing (AA) areshown.

As shown in FIG. 8A, in the first sample S01 and the second sample S02before annealing (BA), the coercivity Hc is approximately 3 Oe to 4 Oe.Good soft magnetic characteristics are exhibited before annealing (BA).However, before annealing (BA), the MR ratio is low and therefore a highgauge factor cannot be obtained.

In the second sample S02, the coercivity Hc increases to 27 Oe afterannealing (AA). This value is almost equal to the value of the thirdsample S03 using a Co₅₀Fe₅₀ layer including no boron. The increase incoercivity Hc in the second sample S02 after annealing (AA) is due tothe fact that crystallization proceeds in the second sample S02 afterannealing (AA).

On the other hand, in the first sample S01, the coercivity Hc afterannealing (AA) keeps the value before annealing (BA). This is due to thefact that in the first sample S01, crystallization does not proceed andthe amorphous structure is maintained even after annealing (BA).

As shown in FIG. 8B, in the first sample S01, the magnetostrictionconstant λ after annealing (AA) substantially keeps the value beforeannealing (BA).

FIG. 13 is a schematic diagram illustrating characteristics of strainsensing elements.

FIG. 13 shows characteristics of the first to third samples S01 to S03mentioned above in a model way.

As shown in FIG. 13, the coercivity Hc of the Co₄₀Fe₄₀B₂₀ layerincluding a large amount of boron is small before annealing (the firstsample S01 and the second sample S02). On the other hand, the Co₅₀Fe₅₀layer including no boron has a large coercivity Hc.

In the second sample S02, boron of the Co₄₀Fe₄₀B₂₀ layer is diffused tothe cap layer 26 c side during annealing and the boron concentration isreduced; consequently, crystallization proceeds, and the coercivity Hcis increased to a level equal to that of the third sample S03. On theother hand, in the first sample S01, the diffusion of boron issuppressed by the functional layer 25, and the boron concentration inthe Co₄₀Fe₄₀B₂₀ layer is maintained; thus, the progress ofcrystallization is suppressed. Consequently, even after annealing (AA),the coercivity Hc can be kept small at a level equal to that beforeannealing (BA). Consequently, in the first sample S01, a largemagnetostriction constant λ of 20 ppm, a small coercivity Hc ofapproximately 3 Oe, and a high MR ratio of 149% are obtained. Thus, ahigh gauge factor of 4000 or more is obtained.

By combining the second magnetic layer 20 (a magnetization free layer)including boron and the functional layer 25 that suppresses thediffusion of boron in the above manner, even after annealing (AA), theboron content in the magnetization free layer can be maintained and theamorphous structure can be maintained.

Thus, in the embodiment, the second magnetic layer 20 including anamorphous portion and including boron and the functional layer 25 of atleast one of an oxide and a nitride that suppresses the diffusion ofboron are used. Thereby, a high-sensitivity strain sensing element canbe provided.

Examples of the strain sensing element according to the embodiment willnow be described.

For the first electrode E1 and the second electrode E2, at least one ofaluminum (Al), aluminum-copper alloy (Al—Cu), copper (Cu), silver (Ag),and gold (Au) is used, for example. By using such a material with arelatively small electric resistance as the first electrode E1 and thesecond electrode E2, a current can be passed through the strain sensingelement 51 efficiently. A nonmagnetic material may be used for the firstelectrode E1.

The first electrode E1 may include an underlayer (not shown) for thefirst electrode E1, a cap layer (not shown) for the first electrode E1,and a layer of at least one of Al, Al—Cu, Cu, Ag, and Au providedbetween them, for example. Tantalum (Ta)/copper (Cu)/tantalum (Ta) orthe like is used as the first electrode E1, for example. By using Ta asthe underlayer for the first electrode E1, the adhesion between the filmunit 70 and the first electrode E1 is improved, for example. Alsotitanium (Ti), titanium nitride (TiN), or the like may be used as theunderlayer for the first electrode E1.

By using Ta as the cap layer for the first electrode E1, the oxidationof copper (Cu) or the like under the cap layer can be prevented. Alsotitanium (Ti), titanium nitride (TiN), or the like may be used as thecap layer for the first electrode E1.

As the underlayer 10 l, a stacked structure including a buffer layer(not shown) and a seed layer (not shown) may be used, for example. Thebuffer layer eases the roughness of the surface of the first electrodeE1 or the film unit 70, and improves the crystallinity of a layerstacked on the buffer layer, for example. As the buffer layer, at leastone selected from the group consisting of tantalum (Ta), titanium (Ti),vanadium (V), tungsten (W), zirconium (Zr), hafnium (Hf), and chromium(Cr) is used, for example. An alloy including at least one selected fromthese materials may be used as the buffer layer.

The thickness of the buffer layer of the underlayer 10 l is preferablynot less than 1 nm and not more than 10 nm. The thickness of the bufferlayer is more preferably not less than 1 nm and not more than 5 nm. Ifthe thickness of the buffer layer is too small, the buffer effect willbe lost. If the thickness of the buffer layer is too large, thethickness of the strain sensing element 51 will be too large. The seedlayer may be formed on the buffer layer, and may have buffer effect. Inthis case, the buffer layer may be omitted. A Ta layer with a thicknessof 3 nm is used as the buffer layer, for example.

The seed layer of the underlayer 10 l controls the crystal orientationof a layer stacked on the seed layer. The seed layer controls thecrystal grain size of a layer stacked on the seed layer. A metal of thefcc structure (face-centered cubic structure), the hcp structure(hexagonal close-packed structure), or the bcc structure (body-centeredcubic structure) or the like is used as the seed layer.

As the seed layer of the underlayer 10 l, ruthenium (Ru) of the hcpstructure, NiFe of the fcc structure, or Cu of the fcc structure may beused. Thereby, the crystal orientation of a spin valve film on the seedlayer can be made the fcc(111) orientation, for example. A Cu layer witha thickness of 2 nm or a Ru layer with a thickness of 2 nm is used asthe seed layer, for example. When it is attempted to enhance the crystalorientation properties of a layer formed on the seed layer, thethickness of the seed layer is preferably not less than 1 nm and notmore than 5 nm. The thickness of the seed layer is more preferably notless than 1 nm and not more than 3 nm. Thereby, the function as a seedlayer of improving the crystal orientation is exhibited sufficiently.

On the other hand, when it is not necessary to provide a crystalorientation to a layer provided on the seed layer (for example, when anamorphous magnetization free layer is formed, etc.), the seed layer maybe omitted, for example. A Ru layer with a thickness of 2 nm is used asthe seed layer, for example.

The pinning layer 10 p provides unidirectional anisotropy to the firstmagnetic layer 10 (a ferromagnetic layer) formed on the pinning layer 10p, and fixes the magnetization 10 m of the first magnetic layer 10, forexample. An antiferromagnetic layer is used as the pinning layer 10 p,for example. At least one selected from the group consisting of Ir—Mn,Pt—Mn, Pd—Pt—Mn, and Ru—Rh—Mn is used for the pinning layer 10 p, forexample. The thickness of the pinning layer 10 p is appropriately set toprovide unidirectional anisotropy of a sufficient strength.

When PtMn or PdPtMn is used as the pinning layer 10 p, the thickness ofthe pinning layer 10 p is preferably not less than 8 nm and not morethan 20 nm. The thickness of the pinning layer 10 p is more preferablynot less than 10 nm and not more than 15 nm. When IrMn is used as thepinning layer 10 p, unidirectional anisotropy can be provided by asmaller thickness than when PtMn is used as the pinning layer 10 p. Inthis case, the thickness of the pinning layer 10 p is preferably notless than 4 nm and not more than 18 nm. The thickness of the pinninglayer 10 p is more preferably not less than 5 nm and not more than 15nm. An Ir₂₂Mn₇₈ layer with a thickness of 7 nm is used as the pinninglayer 10 p, for example.

A hard magnetic layer may be used as the pinning layer 10 p. As the hardmagnetic layer, CoPt (the ratio of Co being not less than 50 at. % andnot more than 85 at. %), (Co_(x)Pt_(100-x))_(100-y)Cr_(y) (x being notless than 50 at. % and not more than 85 at. %, y being not less than 0at. % and not more than 40 at. %), FePt (the ratio of Pt being not lessthan 40 at. % and not more than 60 at. %), or the like may be used, forexample.

As the second magnetization pinned layer 10 b, Co_(x)Fe_(100-x) alloy (xbeing not less than 0 at. % and not more than 100 at. %),Ni_(x)Fe_(100-x) alloy (x being not less than 0 at. % and not more than100 at. %), or a material in which a nonmagnetic element is added tothese is used, for example. As the second magnetization pinned layer 10b, at least one selected from the group consisting of Co, Fe, and Ni isused, for example. As the second magnetization pinned layer 10 b, analloy including at least one material selected from these materials maybe used. As the second magnetization pinned layer 10 b,(Co_(x)Fe_(100-x))_(100-y)B_(y) alloy (x being not less than 0 at. % andnot more than 100 at. %, y being not less than 0 at. % and not more than30 at. %) may be used. By using an amorphous alloy of(Co_(x)Fe_(100-x))_(100-y)B_(y) as the second magnetization pinned layer10 b, the variation in characteristics of the strain sensing element 51can be suppressed even when the size of the strain sensing element 51 issmall.

The thickness of the second magnetization pinned layer 10 b ispreferably not less than 1.5 nm and not more than 5 nm, for example.Thereby, the strength of the unidirectional anisotropic magnetic fieldcaused by the pinning layer 10 p can be increased, for example. Thestrength of the antiferromagnetic coupling magnetic field between thesecond magnetization pinned layer 10 b and the first magnetizationpinned layer 10 a can be increased via the magnetic coupling layer 10 cformed on the second magnetization pinned layer 10 b, for example. Themagnetic thickness (the product of the saturation magnetization Bs andthe thickness t (Bs·t)) of the second magnetization pinned layer 10 b ispreferably substantially equal to the magnetic thickness of the firstmagnetization pinned layer 10 a, for example.

The saturation magnetization of Co₄₀Fe₄₀B₂₀ in a thin film form isapproximately 1.9 T (tesla). When a Co₄₀Fe₄₀B₂₀ layer with a thicknessof 3 nm is used as the first magnetization pinned layer 10 a, themagnetic thickness of the first magnetization pinned layer 10 a is 1.9T×3 nm, which is 5.7 T nm, for example. On the other hand, thesaturation magnetization of Co₇₅Fe₂₅ is approximately 2.1 T. Thethickness of the second magnetization pinned layer 10 b by which amagnetic thickness equal to the above is obtained is 5.7 T nm/2.1 T,which is 2.7 nm. In this case, a Co₇₅Fe₂₅ layer with a thickness ofapproximately 2.7 nm is preferably used as the second magnetizationpinned layer 10 b. A Co₇₅Fe₂₅ layer with a thickness of 2.5 nm is usedas the second magnetization pinned layer 10 b, for example.

In the strain sensing element 51, a synthetic pin structure composed ofthe second magnetization pinned layer 10 b, the magnetic coupling layer10 c, and the first magnetization pinned layer 10 a is used as the firstmagnetic layer 10. A single pin structure formed of one magnetizationpinned layer may be used as the first magnetic layer 10. In the casewhere a single pin structure is used, a Co₄₀Fe₄₀B₂₀ layer with athickness of 3 nm is used as the magnetization pinned layer, forexample. The same material as the material of the second magnetizationpinned layer 10 b described above may be used as the ferromagnetic layerused as the magnetization pinned layer of the single pin structure.

The magnetic coupling layer 10 c produces an antiferromagnetic couplingbetween the second magnetization pinned layer 10 b and the firstmagnetization pinned layer 10 a. The magnetic coupling layer 10 c formsa synthetic pin structure. Ru is used as the magnetic coupling layer 10c, for example. The thickness of the magnetic coupling layer 10 c ispreferably not less than 0.8 nm and not more than 1 nm, for example.Other materials than Ru may be used as the magnetic coupling layer 10 cto the extent that they produce a sufficient antiferromagnetic couplingbetween the second magnetization pinned layer 10 b and the firstmagnetization pinned layer 10 a. The thickness of the magnetic couplinglayer 10 c may be set to a thickness of not less than 0.8 nm and notmore than 1 nm corresponding to the second peak (2nd peak) of the RKKY(Ruderman-Kittel-Kasuya-Yosida) coupling. The thickness of the magneticcoupling layer 10 c may be set to a thickness of not less than 0.3 nmand not more than 0.6 nm corresponding to the first peak (1st peak) ofthe RKKY coupling. Ru with a thickness of 0.9 nm is used as the magneticcoupling layer 10 c, for example. Thereby, a highly reliable coupling isobtained more stably.

The magnetic layer used as the first magnetization pinned layer 10 adirectly contributes to the MR effect. Co—Fe—B alloy is used as thefirst magnetization pinned layer 10 a, for example. Specifically,(Co_(x)Fe_(100-x))_(100-y)B_(y) alloy (x being not less than 0 at. % andnot more than 100 at. %, y being not less than 0 at. % and not more than30 at. %) may be used as the first magnetization pinned layer 10 a. Whenan amorphous alloy of (Co_(x)Fe_(100-x))_(100-y)B_(y) is used as thefirst magnetization pinned layer 10 a, the variation between elementsdue to crystal grains can be suppressed even when the size of the strainsensing element 51 is small, for example.

A layer (for example, a tunnel insulating layer (not shown)) formed onthe first magnetization pinned layer 10 a may be planarized. By theplanarization of the tunnel insulating layer, the defect density of thetunnel insulating layer can be reduced. Thereby, a larger MR ratio isobtained with a lower resistance-area product (RA). When Mg—O is used asthe material of the tunnel insulating layer, an amorphous alloy of(Co_(x)Fe_(100-x))_(100-y)B_(y) may be used as the first magnetizationpinned layer 10 a; thereby, the (100) orientation properties of the Mg—Olayer formed on the tunnel insulating layer can be enhanced, forexample. By enhancing the (100) orientation properties of the MgO layer,a larger MR ratio is obtained. The (Co_(x)Fe_(100-x))_(100-y)B_(y) alloyis crystallized during annealing, with the (100) plane of the Mg—O layeras a template. Thus, good crystal matching between the Mg—O and the(Co_(x)Fe_(100-x))_(100-y)B_(y) alloy is obtained. By obtaining goodcrystal matching, a larger MR ratio is obtained.

As the first magnetization pinned layer 10 a, Fe—Co alloy may be used aswell as Co—Fe—B alloy, for example.

When the first magnetization pinned layer 10 a is thicker, a larger MRratio is obtained. To obtain a larger fixed magnetic field, the firstmagnetization pinned layer 10 a is preferably thinner. Between the MRratio and the fixed magnetic field, there is a trade-off in thethickness of the first magnetization pinned layer 10 a. When Co—Fe—Balloy is used as the first magnetization pinned layer 10 a, thethickness of the first magnetization pinned layer 10 a is preferably notless than 1.5 nm and not more than 5 nm. The thickness of the firstmagnetization pinned layer 10 a is more preferably not less than 2.0 nmand not more than 4 nm.

For the first magnetization pinned layer 10 a, Co₉₀Fe₁₀ alloy of the fccstructure, Co of the hcp structure, or a Co alloy of the hcp structureis used as well as the material described above. As the firstmagnetization pinned layer 10 a, at least one selected from the groupconsisting of Co, Fe, and Ni is used, for example. As the firstmagnetization pinned layer 10 a, an alloy including at least onematerial selected from these materials is used. As the firstmagnetization pinned layer 10 a, an FeCo alloy material of the bccstructure, a Co alloy with a cobalt content of 50 at. % or more, or amaterial with a Ni content of 50 at. % or more (a Ni alloy) may be used;thereby, a larger MR ratio is obtained, for example.

As the first magnetization pinned layer 10 a, a Heusler magnetic alloylayer of Co₂MnGe, Co₂FeGe, Co₂MnSi, Co₂FeSi, Co₂MnAl, Co₂FeAl,Co₂MnGa_(0.5)Ge_(0.5), Co₂FeGa_(0.5)Ge_(0.5), and the like may be used,for example. As the first magnetization pinned layer 10 a, a Co₄₀Fe₄₀B₂₀layer with a thickness of 3 nm is used, for example.

The spacer layer 30 cuts the magnetic coupling between the firstmagnetic layer 10 and the second magnetic layer 20, for example. Ametal, an insulator, or a semiconductor is used for the spacer layer 30,for example. Cu, Au, Ag, or the like is used as the metal, for example.In the case where a metal is used as the spacer layer 30, the thicknessof the spacer layer is approximately not less than 1 nm and not morethan 7 nm, for example. As the insulator or the semiconductor, amagnesium oxide (Mg—O etc.), an aluminum oxide (Al₂O₃ etc.), a titaniumoxide (Ti—O etc.), a zinc oxide (Zn—O etc.), a gallium oxide (Ga—O), orthe like is used, for example. In the case where an insulator or asemiconductor is used as the spacer layer 30, the thickness of thespacer layer 30 is approximately not less than 0.6 nm and not more than2.5 nm, for example. A CCP (current-confined-path) spacer layer may beused as the spacer layer 30, for example. In the case where a CCP spacerlayer is used as the spacer layer, a structure is used in which a copper(Cu) metal path is formed in an insulating layer of aluminum oxide(Al₂O₃), for example. A Mg—O layer with a thickness of 1.6 nm is used asthe spacer layer 30, for example.

For the second magnetic layer 20, a ferromagnetic material is be used.In the embodiment, a high gauge factor can be obtained by using aferromagnetic material of an amorphous structure including boron as thesecond magnetic layer 20. For the second magnetic layer 20, an alloyincluding at least one element selected from the group consisting of Fe,Co, and Ni and boron (B) may be used. For the second magnetic layer 20,Co—Fe—B alloy, Fe—B alloy, Fe—Co—Si—B alloy, or the like may be used,for example. For the second magnetic layer 20, an alloy including atleast one element selected from the group consisting of Fe, Co, and Niand boron (B) may be used. As the second magnetic layer 20, aCo₄₀Fe₄₀B₂₀ layer with a thickness of 4 nm may be used, for example.

The second magnetic layer 20 may have a multiple-layer structure. Thesecond magnetic layer 20 may have a two-layer structure, for example.When a tunnel insulating layer of Mg—O is used as the spacer layer 30,it is preferable that a layer of Co—Fe—B alloy or Fe—B alloy be providedin a portion in contact with the spacer layer 30 of the second magneticlayer 20. Thereby, a high magnetoresistance effect is obtained.

The second magnetic layer 20 includes a first portion on the spacerlayer 30 side and a second portion on the functional layer 25 side, forexample. The first portion includes a portion in contact with the spacerlayer 30 of the second magnetic layer 20, for example. A layer ofCo—Fe—B alloy is used as the first portion. Fe—B alloy is used for thesecond portion, for example. That is, Co—Fe—B/Fe—B alloy is used as thesecond magnetic layer 20, for example. The thickness of the Co₄₀Fe₄₀B₂₀layer is 0.5 nm, for example. The thickness of the Fe—B alloy layermentioned above used as the second magnetic layer 20 is 6 nm, forexample.

In the embodiment, a high gauge factor can be obtained by using aferromagnetic material including boron and including an amorphousportion as the second magnetic layer 20. Examples of the material thatmay be used for the second magnetic layer 20 are described later.

In the embodiment, an oxide or a nitride may be used for the functionallayer 25. A Mg—O layer with a thickness of 1.5 nm may be used as thefunctional layer 25, for example. In the embodiment, by using an oxidelayer or a nitride layer as the functional layer 25, the diffusion ofboron included in the second magnetic layer 20 is suppressed, forexample. Thereby, the amorphous structure in the second magnetic layer20 can be maintained. Consequently, a high gauge factor can be obtained.Examples of the material that may be used for the functional layer 25are described later.

The cap layer 26 c protects a layer provided under the cap layer 26 c. Aplurality of metal layers are used as the cap layer 26 c, for example. Atwo-layer structure of a Ta layer and a Ru layer (Ta/Ru) is used as thecap layer 26 c, for example. The thickness of the Ta layer is 1 nm, forexample, and the thickness of the Ru layer is 5 nm, for example. Othermetal layers may be provided as the cap layer 26 c in place of the Talayer and the Ru layer. The configuration of the cap layer 26 c isarbitrary. A nonmagnetic material may be used as the cap layer 26 c, forexample. Other materials may be used as the cap layer 26 c to the extentthat they can protect a layer provided under the cap layer 26 c.

Examples of the configuration and material of the second magnetic layer20 (a magnetization free layer) are further described.

For the second magnetic layer 20, an alloy including at least oneelement selected from Fe, Co, and Ni and boron (B) may be used. Co—Fe—Balloy, Fe—B alloy, or the like may be used for the second magnetic layer20, for example. (Co_(x)Fe_(100-x))_(100-y)B_(y) alloy (x being not lessthan 0 at. % and not more than 100 at. %, y being larger than 0 at. %and not more than 40 at. %) may be used for the second magnetic layer20, for example. A Co₄₀Fe₄₀B₂₀ layer with a thickness of 4 nm may beused as the second magnetic layer 20, for example.

In the case where an alloy including at least one element selected fromthe group consisting of Fe, Co, and Ni and boron (B) is used for thesecond magnetic layer 20, at least one of Ga, Al, Si, and W may be addedas an element that facilitates the increase in magnetostriction constantλ. Fe—Ga—B alloy, Fe—Co—Ga—B alloy, or Fe—Co—Si—B alloy may be used asthe second magnetic layer 20, for example.

When Fe_(1-y)B_(y) (0<y≤0.3) or (Fe_(a)X_(1-a))_(1-y)B_(y) (X being Coor Ni; 0.8≤a<1, 0<y≤0.3) is used as at least part of the second magneticlayer 20, a large magnetostriction constant λ and a low coercivity arewell balanced easily; thus, this case is particularly preferable. AnFe₈₀B₂₀ layer with a thickness of 4 nm may be used, for example.

The second magnetic layer 20 includes an amorphous portion as mentionedabove. Part of the second magnetic layer 20 may be crystallized. Thesecond magnetic layer 20 may include both a crystallized portion and anamorphous portion.

The magnetostriction constant λ and the coercivity Hc in themagnetization free layer are summable properties in accordance with thevolume ratio of the ferromagnetic material included in the magnetizationfree layer. Even when a crystallized portion exists in the magnetizationfree layer, a small coercivity Hc can be obtained because the magneticproperties of the amorphous portion are obtained. In the case where atunneling magnetoresistance effect using an insulator for the spacerlayer 30 is used, it is preferable that a portion including theinterface with the spacer layer 30 of the second magnetic layer 20 becrystallized, for example. Thereby, a high MR ratio is obtained, forexample.

The boron concentration (for example, the composition ratio of boron) inthe second magnetic layer 20 is preferably 5 at. % (atomic percent) ormore. Thereby, it becomes easy to obtain an amorphous structure. Theboron concentration in the second magnetic layer 20 is preferably 35 at.% or less. If the boron concentration is too high, the magnetostrictionconstant is reduced, for example. The boron concentration in the secondmagnetic layer 20 is preferably not less than 5 at. % and not more than35 at. %, and more preferably not less than 10 at. % and not more than30 at. %, for example.

The second magnetic layer 20 includes a first portion on the spacerlayer 30 side and a second portion on the functional layer 25 side, forexample. The first portion includes a portion in contact with the spacerlayer 30 of the second magnetic layer 20, for example. A layer ofCo—Fe—B alloy is used as the first portion. Fe—Ga—B alloy is used forthe second portion, for example. That is, Co—Fe—B/Fe—Ga—B alloy is usedas the second magnetic layer 20, for example. The thickness of theCo₄₀Fe₄₀B₂₀ layer is 2 nm, for example. The thickness of the Fe—Ga—Blayer is 6 nm, for example. Also Co—Fe—B/Fe—B alloy may be used. Thethickness of the Co₄₀Fe₄₀B₂₀ is 0.5 nm, for example. The thickness ofthe Fe—B is 4 nm, for example. As described above, Co—Fe—B/Fe—B alloymay be used as the second magnetic layer 20, for example. In this case,the thickness of the Co₄₀Fe₄₀B₂₀ layer is 0.5 nm, for example. Thethickness of the Fe—B layer is 4 nm, for example. Thus, a high MR ratiocan be obtained by using Co—Fe—B alloy for the first portion on thespacer layer 30 side.

Crystallized Fe₅₀Co₅₀ (thickness: 0.5 nm) may be used for the firstportion including the interface with the spacer layer 30 of the secondmagnetic layer 20. A two-layer structure such as crystallized Fe₅₀Co₅₀(thickness: 0.5 nm)/Co₄₀Fe₄₀B₂₀ (thickness: 2 nm) may be used as thefirst portion including the interface with the spacer layer 30 of thesecond magnetic layer 20.

Also a stacked film of Fe₅₀Co₅₀ (thickness: 0.5 nm)/Co₄₀Fe₄₀B₂₀(thickness: 4 nm) may be used as the second magnetic layer 20. Also astacked film of Fe₅₀Co₅₀ (thickness: 0.5 nm)/Co₄₀Fe₄₀B₂₀ (thickness: 2nm)/Co₃₅Fe₃₅B₃₀ (thickness: 4 nm) may be used as the second magneticlayer 20. In this stacked film, the boron concentration increases withdistance from the spacer layer 30.

FIG. 14 is a schematic diagram illustrating the strain sensing elementaccording to the first embodiment.

FIG. 14 illustrates the distribution of boron concentration in thestrain sensing element 50 (the strain sensing element 51) according tothe embodiment.

As shown in FIG. 14, the second magnetic layer 20 includes a firstportion 20 p and a second portion 20 q. The first portion 10 p isprovided between the spacer layer 30 and the second portion 20 q. Thefirst portion 20 p includes a portion in contact with the spacer layer30 of the second magnetic layer 20, for example. The second portion 20 qincludes a portion in contact with the functional layer 25 of the secondmagnetic layer 20, for example.

As shown in FIG. 14, by reducing the boron concentration C_(B) of thefirst portion 20 p of the second magnetic layer 20 (a portion on thespacer layer 30 side), the MR ratio in the first portion 20 p can beimproved. Thereby, the change in electric resistance R with respect tothe change in magnetization direction can be increased, and a high gaugefactor can be obtained. On the other hand, by increasing the boronconcentration C_(B) in the second portion 20 q (a portion away from thespacer layer 30), the coercivity Hc can be reduced in the second portion20 q, and the coercivity Hc of the whole second magnetic layer 20 can bereduced.

In the case where a tunneling magnetoresistance effect using Mg—O or thelike for the spacer layer is used, the MR ratio depends on thecomposition and crystal structure of the magnetic material with athickness of approximately 0.5 nm in contact with the spacer layer. Inother words, the MR ratio is determined only by the magnetic layer nearthe spacer layer. On the other hand, in the case where the magnetizationfree layer is a stacked film, features in accordance with the thicknessof the layers included in the stacked film, for example features of thethickest layer, are reflected most strongly in the magnetic propertiessuch as magnetostriction and coercivity. This is because the stackedbody of the magnetic materials included in the magnetization free layeris exchange-coupled and averaged. In the embodiment, a layer of amagnetic material having crystallinity is provided near the spacerlayer, for example. Thereby, a high MR ratio is obtained. On the otherhand, a layer of an amorphous magnetic material including boron isprovided in the second portion 20 q not in contact with the spacerlayer. Thereby, a low coercivity is obtained. Thus, a low coercivity canbe obtained as well as a high MR ratio.

Information on such a distribution of boron concentration C_(B) isobtained by SIMS analysis (secondary ion mass spectrometry), forexample. This information is obtained by the combination ofcross-sectional TEM and EELS. This information is obtained by EELSanalysis. This information is obtained also by three-dimensional atomprobe analysis.

The thickness of the first portion 20 p (a portion with a relativelyhigh level of crystallization) is smaller than the thickness of thesecond portion 20 q (a portion with a relatively low level ofcrystallization, an amorphous portion), for example. Thereby, it becomeseasy to obtain a small coercivity Hc, for example. The thickness of thefirst portion 20 p is not more than ⅓ of the thickness of the secondportion 20 q, for example.

A fourth sample S04 will now be described. In the fourth sample S04, theboron concentration in the first portion 20 p of the second magneticlayer 20 is set lower than the boron concentration in the second portion20 q.

The material and thickness of the layers included in the fourth sampleS04 are as follows:

The underlayer 10 l: Ta (1 nm)/Ru (2 nm)

The pinning layer 10 p: Ir₂₂Mn₇₈ (7 nm)

The second magnetization pinned layer 10 b: Co₇₅Fe₂₅ (2.5 nm)

The magnetic coupling layer 10 c: Ru (0.9 nm)

The first magnetization pinned layer 10 a: Co₄₀Fe₄₀B₂₀ (3 nm)

The spacer layer 30: Mg—O (1.6 nm)

The second magnetic layer 20: Co₅₀Fe₅₀ (0.5 nm)/Co₄₀Fe₄₀B₂₀ (8 nm)

The functional layer 25: Mg—O (1.5 nm)

The cap layer 26 c: Cu (1 nm)/Ta (2 nm)/Ru (5 nm)

In the fourth sample S04, Co₅₀Fe₅₀ (0.5 nm)/Co₄₀Fe₄₀B₂₀ (8 nm) is usedas the magnetization free layer, and the first portion 20 p with a lowboron concentration and the second portion 20 q with a high boronconcentration are provided in the magnetization free layer.

Investigation results of the fourth sample S04 will now be described.

FIG. 15 is a microscope photographic image illustrating characteristicsof a strain sensing element.

FIG. 15 is a cross-sectional transmission electron microscopephotographic image of the strain sensing element of the fourth sampleS04.

As can be seen from FIG. 15, in the second magnetic layer 20, the firstportion 20 p on the spacer layer 30 side has a crystal structure. It isfound that the second portion 20 q on the functional layer 25 side hasan amorphous structure.

FIG. 16A and FIG. 16B are schematic diagrams illustratingcharacteristics of the strain sensing element.

FIG. 16B corresponds to part of FIG. 15A.

FIG. 16A is investigation results of the depth profile of elements ofthe fourth sample S04 obtained by EELS. FIG. 16A shows the depth profileof elements on line L3 shown in FIG. 15A.

As can be seen from FIG. 16A, it is found that boron of themagnetization free layer (the second magnetic layer) is not diffused toother layers but remains in the magnetization free layer by providingthe functional layer 25, similarly to the first sample S01. The EELSintensity of boron in the first portion 20 p on the spacer layer 30 sideof the magnetization free layer is lower than the EELS intensity ofboron in the second portion 20 q on the functional layer 25 side.

The MR ratio of the fourth sample S04 is 187%. The MR ratio of thefourth sample S04 is higher than the MR ratio of the first sample S01.The MR ratio is improved in the fourth sample S04. This is presumed tobe due to the fact that the first portion 20 p having crystallinity isprovided on the spacer layer 30 (a Mg—O layer) side. In the fourthsample S04, the gauge factor can be improved by the high MR ratio.

In the fourth sample S04, the magnetostriction is 20 ppm, and thecoercivity is 3.8 Oe. From the results, even when the first portion 20 phaving crystallinity is provided, a low coercivity can be achieved byproviding the second portion 20 q of an amorphous structure. Themagnetic properties in the second magnetic layer 20 are the sum of themagnetic properties of the first portion 20 p and the magneticproperties of the second portion 20 q, for example.

For the functional layer 25, an oxide material or a nitride material isused. In the oxide material or the nitride material, atoms arechemically bonded. Therefore, the effect of suppressing the diffusion ofboron is high. A Mg—O layer with a thickness of 2.0 nm may be used asthe functional layer 25, for example.

As the oxide material or the nitride material used for the functionallayer 25, an oxide material including at least one element selected fromthe first group consisting of Mg, Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu,Zn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Sn, Cd, and Ga or a nitridematerial including at least one element selected from the first groupmay used, as described above.

The functional layer 25 does not contribute to the magnetoresistanceeffect. Hence, the resistance-area product (RA) of the functional layer25 is preferably low. The resistance-area product (RA) of the functionallayer 25 is preferably lower than the resistance-area product (RA) ofthe spacer layer 30 contributing to the magnetoresistance effect, forexample. For the functional layer 25, an oxide including at least oneelement selected from the group consisting of Mg, Ti, V, Zn, Sn, Cd, andGa or a nitride including the element is used, for example. The barrierheight of oxides or nitrides of these elements is low. Theresistance-area product (RA) of the functional layer 25 can be reducedby using an oxide or a nitride of these elements.

It is more preferable to use an oxide for the functional layer 25.Chemical bonds in oxides are stronger than chemical bonds in nitrides.The diffusion of boron can be suppressed more effectively by using anoxide for the functional layer 25, for example.

In the specification of this application, oxynitrides are included ineither of oxides and nitrides. In the case where the ratio of oxygen ishigher than the ratio of nitrogen in an oxynitride, the oxynitride canbe included in oxides, for example. In the case where the ratio ofnitrogen is higher than the ratio of oxygen in an oxynitride, theoxynitride can be included in nitrides, for example.

In the case where an oxide or a nitride is used for the functional layer25, the thickness of the functional layer 25 is preferably 0.5 nm ormore. Thereby, the diffusion of boron is suppressed effectively, forexample. The thickness of the functional layer 25 is preferably 5 nm orless. Thereby, the resistance-area product (RA) can be reduced, forexample. The thickness of the functional layer 25 is preferably not lessthan 0.5 nm and not more than 5 nm, and more preferably not less than 1nm and not more than 3 nm. The thickness of the functional layer 25 maybe 2 nm or more.

Another metal layer or the like may be interposed between the secondmagnetic layer 20 and the functional layer 25. If the distance betweenthe second magnetic layer 20 and the functional layer 25 is too long,boron may be diffused in the region between them, and the boronconcentration of the second magnetic layer 20 may be reduced, forexample. The distance between the second magnetic layer 20 and thefunctional layer 25 is preferably 10 nm or less, and more preferably 3nm or less, for example.

FIG. 17A to FIG. 17E are schematic views illustrating other strainsensing elements according to the first embodiment.

As shown in FIG. 17A, in a strain sensing element 52 a according to theembodiment, a magnetic layer 27 is further provided. The functionallayer 25 is disposed between the magnetic layer 27 and the secondmagnetic layer 20. The magnetization of the magnetic layer 27 (thedirection thereof) is variable. The material and configuration describedin regard to the second magnetic layer 20 may be used for the magneticlayer 27. The magnetic layer 27 and the second magnetic layer 20 may beintegrated together to function as a magnetization free layer.

When the magnetic layer 27 and the second magnetic layer 20 are regardedas a magnetization free layer, the functional layer 25 can be regardedas being provided in the magnetization free layer. Also in this case, bythe functional layer 25, the diffusion of boron from the second magneticlayer 20 can be suppressed, and a small coercivity Hc is obtained.Although it is presumed that in the magnetic layer 27 boron is diffusedand an increase in coercivity Hc occurs, the coercivity Hc as the wholemagnetization free layer can be kept small. Thus, the functional layer25 may be provided in the magnetization free layer. In the case wherethe functional layer 25 is provided in the magnetization free layer, astacked film including a plurality of layers may be used as thefunctional layer 25.

As shown in FIG. 17B to FIG. 17E, in strain sensing elements 52 b to 52e according to the embodiment, the functional layer 25 is provided inthe second magnetic layer 20. Also in this case, a high gauge factor isobtained.

In the strain sensing element 52 c illustrated in FIG. 17C, twofunctional layers 25 are provided in the second magnetic layer 20. Thenumber of functional layers 25 may be 3 or more.

In the strain sensing element 52 d illustrated in FIG. 17D, onefunctional layer 25 is provided on the cap layer side. Furthermore, afunctional layer 25 is provided in the second magnetic layer 20.

In the strain sensing element 52 e illustrated in FIG. 17E, onefunctional layer 25 is provided on the cap layer side. Furthermore, aplurality of functional layers 25 are provided in the second magneticlayer 20. The number of functional layers 25 may be 3 or more.

As shown in FIGS. 17A to 17E, the MR ratio in the first portion 20 p canbe improved by reducing the boron concentration CB in the first portion20 p of the second magnetic layer 20 (a portion on the spacer layer 30side). Thereby, the change in electric resistance R with respect to thechange in magnetization direction can be increased, and a high gaugefactor can be obtained. On the other hand, by increasing the boronconcentration CB in the second portion 20 q (a portion away from thespacer layer 30), the coercivity Hc can be reduced in the second portion20 q, and the coercivity Hc of the whole second magnetic layer 20 can bereduced. As shown in FIGS. 17C to 17E, in the case where there are aplurality of functional layers 25, a layer in the second magnetic layer20 that is located farther from the spacer layer than the first portion20 p and located further to the spacer layer 30 side than any one of theplurality of functional layers 25 can be regarded as the second portion20 q.

As mentioned above, the functional layer 25 may be provided in themagnetization free layer. In this case, the diffusion of boron in aportion of the magnetization free layer located between the functionallayer 25 and the spacer layer 30 can be suppressed. Thereby, a smallcoercivity Hc is obtained. That is, the coercivity Hc of the wholemagnetization free layer can be kept small. In the case where thefunctional layer 25 is provided in the magnetization free layer, aplurality of functional layers 25 may be provided.

FIG. 18A to FIG. 18C are schematic diagrams illustrating other strainsensing elements according to the first embodiment.

FIG. 18A is a schematic cross-sectional view showing a strain sensingelement 52 f according to the embodiment. FIG. 18B illustrates thedistribution of boron concentration in the strain sensing element 52 f.

As shown in FIG. 18A, the second magnetic layer 20 includes a magneticfilm 21 a, a magnetic film 21 b, and a nonmagnetic film 21 c. Thenonmagnetic film 21 c is disposed between the magnetic film 21 a and themagnetic film 21 b. The magnetic film 21 a is disposed between thesecond magnetic film 21 b and the spacer layer 30. A nonmagneticmaterial is used for the nonmagnetic film 21 c.

For the magnetic film 21 a, Co₄₀Fe₄₀B₂₀ is used, for example. Thethickness of the magnetic film 21 a is 1.5 nm or more, and is 2.5 nm,for example. For the magnetic film 21 b, Co₃₅Fe₃₅B₃₀ is used, forexample. The thickness of the magnetic film 21 b is not less than 3 nmand not more than 5 nm, for example. For the nonmagnetic film 21 c, Ruis used, for example. The thickness of the nonmagnetic film 21 c is notless than 0.4 nm and not more than 1.2 nm.

The magnetization of the magnetic film 21 b and the magnetization of themagnetic film 21 a work together. The magnetic film 21 b and themagnetic film 21 a work in an integrated manner. The stacked body of themagnetic film 21 a, the magnetic film 21 b, and the nonmagnetic film 21c forms a magnetization free layer. When the thickness of thenonmagnetic film 21 c is, for example, approximately 1.2 nm or less, themagnetization of the magnetic film 21 b and the magnetization of themagnetic film 21 a work together.

FIG. 18C is a schematic cross-sectional view showing a strain sensingelement 52 g according to the embodiment.

As shown in FIG. 18C, the second magnetic layer 20 includes the magneticfilm 21 a, the nonmagnetic film 21 c, the magnetic film 21 b, anonmagnetic film 21 e, and a magnetic film 21 d. These films are stackedin this order. The configuration described in regard to the magneticfilm 21 a may be used for the magnetic film 21 d, for example. Theconfiguration described in regard to the nonmagnetic film 21 c may beused for the nonmagnetic film 21 e. Thus, a plurality of nonmagneticfilms may be provided in the second magnetic layer 20. The number ofnonmagnetic films in the second magnetic layer 20 may be 3 or more.

In the embodiment, the spacer layer 30 may have a stacked structure. Thespacer layer 30 may include a first nonmagnetic film and a secondnonmagnetic film, for example. The second nonmagnetic film is providedbetween the first nonmagnetic film and the second magnetic layer 20. AMg—O film is provided in the first nonmagnetic film, for example. A filmwith a higher Mg concentration than the first nonmagnetic film is usedas the second nonmagnetic film.

FIG. 19 is a schematic perspective view illustrating another strainsensing element according to the first embodiment.

As illustrated in FIG. 19, an insulating layer 35 is provided in astrain sensing element 53 according to the embodiment. The insulatinglayer 35 (an insulating portion) is provided between the first electrodeE1 and the second electrode E2, for example. The insulating layer 35surrounds the stacked body 10 s between the first electrode E1 and thesecond electrode E2. The insulating layer 35 is provided to oppose theside wall of the stacked body 10 s.

For the insulating layer 35, an aluminum oxide (for example, Al₂O₃), asilicon oxide (for example, SiO₂), or the like may be used, for example.By the insulating layer 35, leakage current around the stacked body 10 scan be suppressed.

FIG. 20 is a schematic perspective view illustrating another strainsensing element according to the first embodiment.

As illustrated in FIG. 20, a hard bias layer 36 is further provided in astrain sensing element 54 according to the embodiment. The hard biaslayer 36 (a hard bias portion) is provided between the first electrodeE1 and the second electrode E2. The insulating layer 35 is disposedbetween the hard bias layer 36 and the stacked body 10 s, for example.In this example, the insulating layer 35 extends between the hard biaslayer 36 and the first electrode E1.

By the magnetization of the hard bias layer 36, at least one of themagnetization 10 m of the first magnetic layer 10 and the magnetization20 m of the second magnetic layer 20 is set to a desired direction. Bythe hard bias layer 36, at least one of the magnetization 10 m and themagnetization 20 m can be set to a desired direction in a state where noforce is applied to the strain sensing element.

For the hard bias layer 36, a hard ferromagnetic material with arelatively high magnetic anisotropy such as CoPt, CoCrPt, and FePt isused, for example. As the hard bias layer 36, a structure in which alayer of a soft magnetic material such as FeCo and Fe and anantiferromagnetic layer are stacked may be used. In this case, themagnetization runs along a prescribed direction due to an exchangecoupling. The thickness (for example, the length along the directionfrom the first electrode E1 toward the second electrode E2) of the hardbias layer 36 is not less than 5 nm and not more than 50 nm, forexample.

The hard bias layer 36 and the insulating layer 35 mentioned above canbe used for any one of the strain sensing elements described above andbelow.

FIG. 21 is a schematic perspective view illustrating another strainsensing element according to the first embodiment.

As shown in FIG. 21, another strain sensing element 55 a according tothe embodiment includes the first electrode E1 (for example, a lowerelectrode), the underlayer 10 l, the functional layer 25, the secondmagnetic layer 20 (a magnetization free layer), the spacer layer 30, thefirst magnetization pinned layer 10 a, the magnetic coupling layer 10 c,the second magnetization pinned layer 10 b, the pinning layer 10 p, thecap layer 26 c, and the second electrode E2 (for example, an upperelectrode) that are sequentially aligned. The strain sensing element 55a is a top spin valve type.

As the underlayer 10 l, Ta/Cu is used, for example. The thickness of theTa layer is 3 nm, for example. The thickness of the Ru layer is 5 nm,for example.

As the functional layer 25, Mg—O is used, for example. The thickness ofthe Mg—O layer is 1.5 nm, for example.

As the second magnetic layer 20, Co₄₀Fe₄₀B₂₀ is used, for example.

The thickness of the Co₄₀Fe₄₀B₂₀ layer is 4 nm, for example.

As the spacer layer 30, a Mg—O layer with a thickness of 1.6 nm is used,for example.

As the first magnetization pinned layer 10 a, Co₄₀Fe₄₀B₂₀/Fe₅₀Co₅₀ isused, for example. The thickness of the Co₄₀Fe₄₀B₂₀ layer is 2 nm, forexample. The thickness of the Fe₅₀Co₅₀ layer is 1 nm, for example.

As the magnetic coupling layer 10 c, a Ru layer with a thickness of 0.9nm is used, for example.

As the second magnetization pinned layer 10 b, a Co₇₅Fe₂₅ layer with athickness of 2.5 nm is used, for example.

As the pinning layer 10 p, an IrMn layer with a thickness of 7 nm isused, for example.

As the cap layer 26 c, Ta/Ru is used. The thickness of the Ta layer is 1nm, for example. The thickness of the Ru layer is 5 nm, for example.

The material described in regard to the strain sensing element 51 may beused for the layers included in the strain sensing element 55 a, forexample.

FIG. 22 is a schematic perspective view illustrating another strainsensing element according to the first embodiment.

As shown in FIG. 22, another strain sensing element 55 b according tothe embodiment includes the first electrode E1 (for example, a lowerelectrode), the underlayer 10 l, the pinning layer 10 p, the firstmagnetic layer 10, the spacer layer 30, the second magnetic layer 20,the functional layer 25, the cap layer 26 c, and the second electrode E2(for example, an upper electrode) that are sequentially aligned. Asingle pin structure using a single magnetization pinned layer is usedin the strain sensing element 55 b.

As the underlayer 10 l, Ta/Ru is used, for example. The thickness of theTa layer is 3 nm, for example. The thickness of the Ru layer is 2 nm,for example.

As the pinning layer 10 p, an IrMn layer with a thickness of 7 nm isused, for example.

As the first magnetic layer 10, a Co₄₀Fe₄₀B₂₀ layer with a thickness of3 nm is used, for example.

As the spacer layer 30, a Mg—O layer with a thickness of 1.6 nm is used,for example.

As the second magnetic layer 20, Co₄₀Fe₄₀B₂₀ is used, for example. Thethickness of the Co₄₀Fe₄₀B₂₀ layer is 4 nm, for example.

As the functional layer 25, a Mg—O layer with a thickness of 1.5 nm isused, for example.

As the cap layer 26 c, Ta/Ru is used, for example. The thickness of theTa layer is 1 nm, for example. The thickness of the Ru layer is 5 nm,for example.

The material described in regard to the strain sensing element 51 may beused for the layers included in the strain sensing element 55 b, forexample.

FIG. 23 is a schematic perspective view illustrating another strainsensing element according to the first embodiment.

As shown in FIG. 23, another strain sensing element 55 b according tothe embodiment includes the first electrode E1 (for example, a lowerelectrode), the underlayer 10 l, another functional layer 25 a (a secondfunctional layer), the first magnetic layer 10, the spacer layer 30, thesecond magnetic layer 20, the functional layer 25 (a first functionallayer), the cap layer 26 c, and the second electrode E2 (for example, anupper electrode) that are sequentially aligned. In this example, thefirst magnetic layer 10 is a magnetization free layer, and also thesecond magnetic layer 20 is a magnetization free layer.

As the underlayer 10 l, Ta/Ru is used, for example, The thickness of theTa layer is 3 nm, for example. The thickness of the Ru layer is 5 nm,for example.

As the functional layer 25 a, a Mg—O layer with a thickness of 1.5 nm isused, for example.

As the first magnetic layer 10, a Co₄₀Fe₄₀B₂₀ layer with a thickness of4 nm is used, for example.

As the spacer layer 30, a Mg—O layer with a thickness of 1.6 nm is used,for example.

As the second magnetic layer 20, Co₄₀Fe₄₀B₂₀ is used, for example. Thethickness of the Co₄₀Fe₄₀B₂₀ layer is 4 nm, for example.

As the functional layer 25, a Mg—O layer with a thickness of 1.5 nm isused, for example.

As the cap layer 26 c, Ta/Ru is used, for example. The thickness of theTa layer is 1 nm, for example. The thickness of the Ru layer is 5 nm,for example.

The material described in regard to the strain sensing element 51 may beused for the layers included in the strain sensing element 55 c, forexample. The material and configuration described in regard to thesecond magnetic layer 20 in the stain sensing element 51 may be used forthe first magnetic layer 10 in the strain sensing element 55 c. Thematerial and configuration described in regard to the functional layer25 in the strain sensing element 51 may be used for the functional layer25 a in the strain sensing element 55 c.

In this example, the first magnetic layer 10 may be regarded as thesecond magnetic layer 20, and the functional layer 25 may be regarded asthe functional layer 25 a.

In the case where two magnetization free layers are provided like thestrain sensing element 55 c, the relative angle between themagnetizations of the two magnetization free layers changes inaccordance with the strain ε. Thereby, the element can be made tofunction as a strain sensor. In this case, the value of themagnetostriction of a second magnetization free layer and the value ofthe magnetostriction of a first magnetization free layer may be designedso as to be different from each other. Thereby, the relative anglebetween the magnetizations of the two magnetization free layers changesin accordance with the strain ε.

Second Embodiment

FIG. 24 is a schematic cross-sectional view illustrating a strainsensing element according to a second embodiment.

As shown in FIG. 24, also a strain sensing element 56 according to theembodiment includes a functional layer 25 x, the first magnetic layer10, the second magnetic layer 20, and the spacer layer 30. Thearrangement of these layers is the same as the arrangement described inregard to the first embodiment, and a description is omitted.

In the embodiment, the material used for the functional layer 25 x isdifferent from the material used for the functional layer 25 describedin regard to the first embodiment. Otherwise, the embodiment is similarto the first embodiment. Examples of the functional layer 25 x will nowbe described.

In the strain sensing element 56, for the functional layer 25 x, atleast one selected from the group consisting of magnesium (Mg), silicon(Si), and aluminum (Al) is used, for example. For the functional layer25 x, a material including these light elements is used. These lightelements combine with boron to produce compounds. At least one of a Mg—Bcompound, an Al—B compound, and a Si—B compound is formed in a portionincluding the interface with the second magnetic layer 20 of thefunctional layer 25 x, for example. These compounds suppress thediffusion of boron.

In the embodiment, by providing the functional layer 25 x, the diffusionof boron included in the second magnetic layer 20 can be suppressed, andthe amorphous structure of the second magnetic layer 20 can bemaintained. Consequently, a high gauge factor can be obtained.

Also in the strain sensing element 56 according to the embodiment, thefirst magnetic layer 10 may include the second magnetization pinnedlayer 10 b, the magnetic coupling layer 10 c, and the firstmagnetization pinned layer 10 a described in regard to FIG. 3.

Characteristics of strain sensing elements according to the embodimentwill now be described.

The configuration of a fifth sample is as follows:

The underlayer 10 l: Ta (1 nm)/Ru (2 nm)

The pinning layer 10 p: Ir₂₂Mn₇₈ (7 nm)

The second magnetization pinned layer 10 b: Co₇₅Fe₂₅ (2.5 nm)

The magnetic coupling layer 10 c: Ru (0.9 nm)

The first magnetization pinned layer 10 a: Co₄₀Fe₄₀B₂₀ (3 nm)

The spacer layer 30: Mg—O (1.6 nm)

The second magnetic layer 20: Co₄₀Fe₄₀B₂₀ (4 nm)

The functional layer 25 x: Mg (1.6 nm)

The cap layer 26 c: Cu (1 nm)/Ta (20 nm)/Ru (50 nm)

That is, in the fifth sample, a Mg layer with a thickness of 1.6 nm isused as the functional layer 25 x.

On the other hand, in a sixth sample, a Si layer with a thickness of 0.8nm is used as the functional layer 25 x.

In a seventh sample, the functional layer 25 x is not provided. In theseventh sample, the second magnetic layer 20 is in contact with the caplayer 26 c. The seventh sample is the same as the second sample S02.

Characteristics of these samples have been investigated similarly tothose described in regard to the first sample. The results are asfollows.

In the fifth sample, the MR is 126%, the coercivity Hc is 2.3 Oe, themagnetostriction constant λ is 21 ppm, and the gauge factor is 2861.

In the sixth sample, the MR is 104%, the coercivity Hc is 3.8 Oe, themagnetostriction constant λ is 19 ppm, and the gauge factor is 2091.

In the seventh sample, the MR is 190%, the coercivity Hc is 27 Oe, themagnetostriction constant λ is 30 ppm, and the gauge factor is 895.

Thus, a high gauge factor is obtained by using the functional layer 25x.

The diffusion of boron from the second magnetic layer 20 can besuppressed by providing the functional layer 25 x mentioned above on thesecond magnetic layer 20 including boron. Consequently, a smallcoercivity Hc and a large magnetostriction constant λ are obtained.Thereby, a high gauge factor is obtained.

Characteristics of other strain sensing elements according to theembodiment will now be described.

The configuration of an eighth sample is as follows:

The underlayer 10 l: Ta (1 nm)/Ru (2 nm)

The pinning layer 10 p: Ir₂₂Mn₇₈ (7 nm)

The second magnetization pinned layer 10 b: Co₇₅Fe₂₅ (2.5 nm)

The magnetic coupling layer 10 c: Ru (0.9 nm)

The first magnetization pinned layer 10 a: Co₄₀Fe₄₀B₂₀ (3 nm)

The spacer layer 30: Mg—O (2 nm)

The second magnetic layer 20: described later

The cap layer 26 c: Ta (20 nm)/Ru (50 nm)

In the eighth sample, the stacked film of the second magnetic layer 20that forms a magnetization free layer and the functional layer 25 x hasthe following configuration. Co₄₀Fe₄₀B₂₀ (4 nm)/three layers of thecombination of {Co₄₀Fe₄₀B₂₀ (1 nm)/Si (0.25 nm)}/Co₄₀Fe₄₀B₂₀ (1 nm) isused as the stacked film. The layer of Co₄₀Fe₄₀B₂₀ (4 nm) of the stackedfilm is regarded as the second magnetic layer 20, for example. At leastone of the three Si (0.25 nm) layers of the stacked film is regarded asthe functional layer 25 x.

In a ninth sample, the stacked film of the second magnetic layer 20 thatforms a magnetization free layer and the functional layer 25 x has thefollowing configuration. Co₄₀Fe₄₀B₂₀ (4 nm)/three layers of thecombination of {Co₄₀Fe₄₀B₂₀ (1 nm)/Al (0.25 nm)}/Co₄₀Fe₄₀B₂₀ (1 nm) isused as the stacked film. The layer of Co₄₀Fe₄₀B₂₀ (4 nm) of the stackedfilm is regarded as the second magnetic layer 20, for example. At leastone of the three Al (0.25 nm) layers of the stacked film is regarded asthe functional layer 25 x. In the ninth sample, the configurationexcluding the second magnetic layer 20 and the functional layer 25 x issimilar to the eighth sample.

In a tenth sample, Co₄₀Fe₄₀B₂₀ (4 nm) is used as the second magneticlayer 20 that forms a magnetization free layer. The functional layer 25x is not provided. In the tenth sample, the configuration excluding thesecond magnetic layer 20 and the functional layer 25 x is similar to theeighth sample. That is, the tenth sample is the same as the secondsample S02 mentioned above.

Characteristics of these samples have been investigated similarly tothose described in regard to the first embodiment. The results are asfollows.

In the eighth sample, the MR is 176%, the coercivity Hc is 4.8 Oe, themagnetostriction constant λ is 22 ppm, and the gauge factor is 2849.

In the ninth sample, the MR is 169%, the coercivity Hc is 7.1 Oe, themagnetostriction constant λ is 20 ppm, and the gauge factor is 2195.

In the tenth sample (the seventh sample), the MR is 190%, the coercivityHc is 27 Oe, the magnetostriction constant λ is 30 ppm, and the gaugefactor is 895.

Thus, a high gauge factor is obtained by using the functional layer 25x.

Thus, the diffusion of boron from the magnetization free layer can besuppressed by interposing a layer of a material including at least onelight element selected from the group consisting of Mg, Al, and Si inthe magnetization free layer including boron. Consequently, a smallcoercivity Hc and a large magnetostriction constant λ are obtained.Thereby, a high gauge factor is obtained.

In the embodiment, in the case where a material including at least oneselected from the group consisting of Mg, Al, and Si is used as thefunctional layer 25 x, the thickness of the functional layer 25 x ispreferably 0.5 nm or more, for example. Thereby, the diffusion of boronis suppressed effectively, for example. The thickness of the functionallayer 25 x is preferably 5 nm or less. Thereby, the diffusion of thesurplus Mg, Al, or Si to the second magnetic layer 20 can be suppressed,for example. The thickness of the functional layer 25 x is preferablynot less than 0.5 nm and not more than 5 nm, and preferably not lessthan 1 nm and not more than 3 nm. The thickness of the functional layer25 x may be 2 nm or more.

Another metal layer or the like may be interposed between the functionallayer 25 x and the second magnetic layer 20. If the distance between thefunctional layer 25 x and the second magnetic layer 20 is too long,boron may be diffused in the region between them, and the boronconcentration in the second magnetic layer 20 may be reduced. Thedistance between the functional layer 25 x and the second magnetic layer20 is preferably 10 nm or less, and more preferably 3 nm or less, forexample.

The functional layer 25 x may be provided in the magnetization freelayer as mentioned above. In this case, the diffusion of boron in aportion of the magnetization free layer located between the functionallayer 25 x and the spacer layer 30 can be suppressed. Thereby, a smallcoercivity Hc is obtained. That is, the coercivity Hc of the wholemagnetization free layer can be kept small. In the case where thefunctional layer 25 x is provided in the magnetization free layer, aplurality of functional layers 25 x may be provided.

Third Embodiment

The embodiment relates to a pressure sensor. In the pressure sensor, astrain sensing element of at least one of the first embodiment and thesecond embodiment and modifications thereof is used. In the following,the case where the strain sensing element 50 is used as the strainsensing element is described.

FIG. 25A and FIG. 25B are schematic perspective views illustrating apressure sensor according to a third embodiment.

FIG. 25A is a schematic perspective view. FIG. 25B is a cross-sectionalview taken along line A1-A2 of FIG. 25A.

As shown in FIG. 25A and FIG. 25B, the pressure sensor 110 according tothe embodiment includes the film unit 70 and the strain sensing element50.

The film unit 70 is supported by a support 70 s, for example. Thesupport 70 s is a substrate, for example. The film unit 70 has aflexible region, for example. The film unit 70 is a diaphragm, forexample. The film unit 70 may be integrated with or separated from thesupport 70 s. For the film unit 70, the same material as the support 70s may be used, or a different material from the support 70 s may beused. Part of a substrate that forms the support 70 s may be removed,and a portion of the substrate with a smaller thickness may form thefilm unit 70.

The thickness of the film unit 70 is smaller than the thickness of thesupport 70 s. In the case where the same material is used for the filmunit 70 and the support 70 s and they are integrated together, a portionwith a smaller thickness forms the film unit 70, and a portion with alarger thickness forms the support 70 s.

The support 70 s may have a through hole 70 h penetrating through thesupport 70 s in the thickness direction, and the film unit 70 may beprovided so as to cover the through hole 70 h. At this time, the film ofthe material that forms the film unit 70 may extend also on a portionother than the through hole 70 h of the support 70 s, for example. Atthis time, of the film of the material that forms the film unit 70, aportion overlapping with the through hole 70 h forms the film unit 70.

The film unit 70 has an outer edge 70 r. In the case where the samematerial is used for the film unit 70 and the support 70 s and they areintegrated together, the outer edge of the portion with a smallerthickness is the outer edge 70 r of the film unit 70. In the case wherethe support 70 s has the through hole 70 h penetrating through thesupport 70 s in the thickness direction and the film unit 70 is providedso as to cover the through hole 70 h, the outer edge of the portionoverlapping with the through hole 70 h of the film of the material thatforms the film unit 70 is the outer edge 70 r of the film unit 70.

The support 70 s may continuously support the outer edge 70 r of thefilm unit 70, and may support part of the outer edge 70 r of the filmunit 70.

The strain sensing element 50 is provided on the film unit 70. Thestrain sensing element 50 is provided on part of the film unit 70, forexample. In this example, a plurality of strain sensing elements 50 areprovided on the film unit 70. The number of strain sensing elementsprovided on the film unit may be one.

As shown in FIG. 25B, in the strain sensing element 50, the firstmagnetic layer 10 is disposed between the functional layer 25 and thefilm unit 70, for example. The first magnetic layer 10 is disposedbetween the second magnetic layer 20 and the film unit 70.

In this example, a first interconnection 61 and a second interconnection62 are provided. The first interconnection 61 is connected to the strainsensing element 50. The second interconnection 62 is connected to thestrain sensing element 50. An interlayer insulation film is providedbetween the first interconnection 61 and the second interconnection 62,and the first interconnection 61 and the second interconnection 62 areelectrically insulated, for example. A voltage is applied between thefirst interconnection 61 and the second interconnection 62, and thevoltage is applied to the strain sensing element 50 via the firstinterconnection 61 and the second interconnection 62. When a pressure isapplied to the pressure sensor 110, the film unit 70 is deformed. In thestrain sensing element 50, the electric resistance R changes inaccordance with the deformation of the film unit 70. The pressure can besensed by sensing the change in electric change R via the firstinterconnection 61 and the second interconnection 62.

As the support 70 s, a plate-like substrate may be used, for example. Ahollow portion 71 h (the through hole 70 h) is provided in thesubstrate, for example.

For the support 70 s, a semiconductor material such as silicon, aconductive material such as a metal, or an insulating material may beused, for example. The support 70 s may include silicon oxide, siliconnitride, or the like, for example. The interior of the hollow portion 71h is in a reduced pressure state (vacuum state), for example. Theinterior of the hollow portion 71 h may be filled with a gas such as airor a liquid. The interior of the hollow portion 71 h is designed so thatthe film unit 70 can bend. The interior of the hollow portion 71 h maybe connected to the outside air.

The film unit 70 is provided on the hollow portion 71 h. As the filmunit 70, a portion thinned by processing of a substrate that forms thesupport 70 s is used, for example. The thickness (the length in theZ-axis direction) of the film unit 70 is smaller than the thickness (thelength in the Z-axis direction) of the substrate.

When a pressure is applied to the film unit 70, the film unit isdeformed. The pressure corresponds to the pressure that is to be sensedby the pressure sensor 110. The applied pressure includes pressurecaused by sound waves, ultrasonic waves, or the like. In the case ofsensing pressure caused by sound waves, ultrasonic waves, or the like,the pressure sensor 110 functions as a microphone.

For the film unit 70, an insulating material is used, for example. Thefilm unit 70 includes at least one of silicon oxide, silicon nitride,and silicon oxynitride, for example. A semiconductor material such assilicon may be used for the film unit 70, for example. A metal materialmay be used for the film unit 70, for example.

The thickness of the film unit 70 is not less than 0.1 micrometers (μm)and not more than 3 μm, for example. The thickness is preferably notless than 0.2 μm and not more than 1.5 μm. A stacked body including asilicon oxide film with a thickness of 0.2 μm and a silicon film with athickness of 0.4 μm may be used as the film unit 70, for example.

A plurality of strain sensing elements 50 may be arranged on the filmunit 70. A substantially equal change in electric resistance withrespect to the pressure can be obtained in the plurality of strainsensing elements 50. As described later, the S/N ratio can be increasedby connecting a plurality of strain sensing elements 50 in series or inparallel.

The size of the strain sensing element 50 may be very small. The area ofthe strain sensing element 50 may be sufficiently smaller than the areaof the film unit 70 that is deformed by pressure. The area of the strainsensing element 50 may be not more than ⅕ of the area of the film unit70, for example.

When the diameter of the film unit 70 is approximately 60 μm, thedimension of the strain sensing element 50 may be 12 μm or less, forexample. When the diameter of the film unit 70 is approximately 600 μm,the dimension of the strain sensing element 50 may be 120 μm or less,for example. In view of the processing accuracy of the strain sensingelement 50 etc., it is not necessary to set the dimension of the strainsensing element 50 too small. Thus, the dimension of the strain sensingelement 50 may be set not less than 0.05 μm and not more than 30 μm, forexample.

In this example. the planar shape of the film unit 70 is a circle. Theplanar shape of the film unit 70 may be also an ellipse (for example, aflat circle), a square, a rectangle, a polygon, or a regular polygon,for example.

FIG. 26A to FIG. 26C are schematic diagrams illustrating pressuresensors according to the embodiment. The drawings show examples of theconnection state of a plurality of sensing elements.

As shown in FIG. 26A, in a pressure sensor 116 a according to theembodiment, a plurality of sensing elements 50 are electricallyconnected in series. When the number of sensing elements 50 connected inseries is denoted by N, the electric signal obtained is N times of thatwhen the number of sensing elements 50 is one. On the other hand, thethermal noise and the Schottky noise are N^(1/2) times. That is, the S/Nratio (signal-noise ratio; SNR) is N^(1/2) times. By increasing thenumber N of sensing elements 50 connected in series, the S/N ratio canbe improved without increasing the size of the film unit 70.

A plurality of strain sensing elements 50 provided on the film unit 70may be electrically connected in series. When the number of strainsensing elements 50 connected in series is denoted by N, the electricsignal obtained is N times of that when the number of strain sensingelements 50 is one. On the other hand, the thermal noise and theSchottky noise are N^(1/2) times. That is, the S/N ratio (signal-noiseratio; SNR) is N^(1/2) times. By increasing the number N of strainsensing elements 50 connected in series, the S/N ratio can be improvedwithout increasing the size of the film unit 70.

The bias voltage applied to one strain sensing element is not less than50 millivolts (mV) and not more than 150 mV, for example. When N strainsensing elements 50 are connected in series, the bias voltage is notless than 50 mV×N and not more than 150 mV×N. When the number N ofstrain sensing elements 50 connected in series is 25, the bias voltageis not less than 1 V and not more than 3.75 V, for example.

When the value of the bias voltage is 1 V or more, the design of anelectric circuit that processes the electric signal obtained from thestrain sensing element is easy, and this is preferable in practicalterms.

Bias voltages (inter-terminal voltages) exceeding 10 V are notpreferable in the electric circuit that processes the electric signalobtained from the strain sensing element. In the embodiment, the numberN of strain sensing elements connected in series and the bias voltageare set so that an appropriate voltage range is obtained.

The voltage when the plurality of strain sensing elements areelectrically connected in series is preferably not less than 1 V and notmore than 10 V, for example. The voltage applied between the terminalsof strain sensing elements 50 electrically connected in series (betweenthe terminal of one end and the terminal of the other end) is not lessthan 1 V and not more than 10 V, for example.

To generate this voltage, when the bias voltage applied to one strainsensing element is 50 mV, the number N of strain sensing elements 50connected in series is preferably not less than 20 and not more than200. When the bias voltage applied to one strain sensing element is 150mV, the number N of strain sensing elements connected in series ispreferably not less than 7 and not more than 66.

As shown in FIG. 26B, in a pressure sensor 116 b according to theembodiment, a plurality of sensing elements 50 are electricallyconnected in parallel. In the embodiment, at least part of a pluralityof strain sensing elements 50 may be electrically connected in parallel.

As shown in FIG. 26C, in a pressure sensor 116 c according to theembodiment, a plurality of strain sensing elements 50 may be connectedso as to form a Wheatstone bridge circuit. Thereby, the temperaturecompensation of detected characteristics can be made, for example.

A method for manufacturing a pressure sensor according to the embodimentwill now be described. The following is a method for manufacturing apressure sensor.

FIG. 27A to FIG. 27E are schematic cross-sectional views in order of thesteps, illustrating a method for manufacturing a pressure sensoraccording to the embodiment.

As shown in FIG. 27A, a thin film 70 f is formed on a substrate 71 (forexample, a Si substrate). The substrate 71 forms the support 70 s. Thethin film 70 f forms the film unit 70.

A thin film 70 f of SiO_(x)/Si is formed by sputtering on a Sisubstrate, for example. A SiO_(x) single layer, a SiN single layer, or ametal layer of Al or the like may be used as the thin film 70 f. Aflexible plastic material such as a polyimide and a paraxylene-basedpolymer may be used as the thin film 70 f. An SOI (silicon on insulator)substrate may be used as the substrate 71 and the thin film 70 f. In theSOI, a stacked film of SiO₂/Si is formed on a Si substrate by attachingthe substrates, for example.

As shown in FIG. 27B, the second interconnection 62 is formed. In thisprocess, a conductive film that forms the second interconnection 62 isformed, and the conductive film is processed by photolithography andetching. In the case where the surroundings of the secondinterconnection 62 are filled with an insulating film, lift-off processmay be used. In the lift-off process, after the etching of the patternof the second interconnection 62 and before the peeling of the resist,an insulating film is formed into a film over the entire surface andthen the resist is removed, for example.

As shown in FIG. 27C, strain sensing elements 50 are formed. In thisprocess, a stacked film that forms the strain sensing element 50 isformed, and the stacked film is processed by photolithography andetching. In the case where the space on the side wall of the stackedbody 10 s of the strain sensing element 50 is filled with the insulatinglayer 35, lift-off process may be used. In the lift-off process, afterthe processing of the stacked body 10 s and before the peeling of theresist, the insulating layer 35 is formed into a film over the entiresurface and then the resist is removed, for example.

As shown in FIG. 27D, the first interconnection 61 is formed. In thisprocess, a conductive film that forms the first interconnection 61 isformed, and the conductive film is processed by photolithography andetching. In the case where the surroundings of the first interconnection61 are filled with an insulating film, lift-off process may be used. Inthe lift-off process, after the processing of the first interconnection61 and before the peeling of the resist, an insulating film is formedinto a film over the entire surface and then the resist is removed.

As shown in FIG. 27E, etching is performed from the back surface of thesubstrate 71 to form the hollow portion 71 h. Thereby, the film unit 70and the support 70 s are formed. In the case where a stacked film ofSiO_(x)/Si is used as the thin film 70 f that forms the film unit 70,deep digging processing of the substrate 71 is performed from the backsurface (the lower surface) toward the front surface (the upper surface)of the thin film 70 f, for example. Thereby, the hollow portion 71 h isformed. In the formation of the hollow portion 71 h, a both-surfacealigner exposure apparatus may be used, for example. Thereby, the holepattern of the resist can be formed on the back surface in accordancewith the position of the strain sensing element 50 on the front surface.

In the etching of the Si substrate, the Bosch process using RIE may beused, for example. In the Bosch process, an etching process using SF₆gas and a deposition process using C₄F₈ gas are repeated, for example.Thereby, etching is performed selectively in the depth direction of thesubstrate 71 (the Z-axis direction) while the etching of the side wallof the substrate 71 is suppressed. A SiO_(x) layer is used as the endpoint of the etching, for example. That is, the etching is finishedusing a SiO_(x) layer, which is different in etching selectivity fromSi. The SiO_(x) layer functioning as an etching stopper layer may beused as part of the film unit 70. The SiO_(x) layer may be removed afterthe etching by treatment with anhydrous hydrogen fluoride and analcohol, or the like, etc., for example.

Thus, the pressure sensor 110 according to the embodiment is formed.Other pressure sensors according to the embodiment can be manufacturedby similar methods.

FIG. 28A to FIG. 28C are schematic diagrams illustrating a pressuresensor according to the embodiment. FIG. 28A is a schematic perspectiveview, and FIG. 28B and FIG. 28C are block diagrams illustrating apressure sensor 440.

As shown in FIG. 28A and FIG. 28B, in the pressure sensor 440, a base471, a sensing unit 450, a semiconductor circuit unit 430, an antenna415, an electric interconnection 416, a transmitting circuit 417, and areceiving circuit 417 r are provided.

The antenna 415 is electrically connected to the semiconductor circuitunit 430 via the electric interconnection 416.

The transmitting circuit 417 transmits data based on an electric signaltraveling through the sensing unit 450 wirelessly. At least part of thetransmitting circuit 417 may be provided in the semiconductor circuitunit 430.

The receiving circuit 417 r receives a control signal from an electronicdevice 418 d. At least part of the receiving circuit 417 r may beprovided in the semiconductor circuit unit 430. By providing thereceiving circuit 417 r, the operation of the pressure sensor 440 can becontrolled by operating the electronic device 418 d, for example.

As shown in FIG. 28B, in the transmitting circuit 417, an A/D converter417 a connected to the sensing unit 450 and a Manchester encoding unit417 b may be provided, for example. A switching unit 417 c may beprovided to switch between transmission and reception. In this case, atiming controller 417 d may be provided, and switching in the switchingunit 417 c can be controlled by the timing controller 417 d. A datacorrection unit 417 e, a synchronization unit 417 f, a determinationunit 417 g, and a voltage-controlled oscillator 417 h (VCO) may befurther provided.

As shown in FIG. 28C, a receiving unit 418 is provided in the electronicdevice 418 d used in combination with the pressure sensor 440. As theelectronic device 418 d, an electronic device such as a mobile terminalmay be given, for example.

In this case, the pressure sensor 440 including the transmitting circuit417 and the electronic device 418 d including the receiving unit 418 maybe used in combination.

In the electronic device 418 d, a Manchester encoding unit 417 b, aswitching unit 417 c, a timing controller 417 d, a data correction unit417 e, a synchronization unit 417 f, a determination unit 417 g, avoltage-controlled oscillator 417 h, a memory unit 418 a, and a centralprocessing unit 418 b (CPU) may be provided.

In this example, the pressure sensor 440 further includes a fixing unit467. The fixing unit 467 fixes a film unit 464 (70 d) to the base 471.The fixing unit 467 may have a larger thickness dimension than the filmunit 464 so as to bend less easily even when an external pressure isapplied.

Fixing units 467 may be provided at equal intervals at the edge of thefilm unit 464, for example.

The fixing unit 467 may be provided so as to continuously surround theentire periphery of the film unit 464 (70 d).

The fixing unit 467 may be formed of the same material as the materialof the base 471, for example. In this case, the fixing unit 467 may beformed of silicon or the like, for example.

The fixing unit 467 may be formed of the same material as the materialof the film unit 464 (70 d), for example.

A method for manufacturing a pressure sensor according to the embodimentwill now be described.

FIG. 29A, FIG. 29B, FIG. 30A, FIG. 30B, FIG. 31A, FIG. 31B, FIG. 32A,FIG. 32B, FIG. 33A, FIG. 33B, FIG. 34A, FIG. 34B, FIG. 35A, FIG. 35B,FIG. 36A, FIG. 36B, FIG. 37A, FIG. 37B, FIG. 38A, FIG. 38B, FIG. 39A,FIG. 39B, FIG. 40A, and FIG. 40B are schematic views illustrating amethod for manufacturing a pressure sensor according to the embodiment.

FIG. 29A to FIG. 40A are schematic plan views, and FIG. 29B to FIG. 40Bare schematic cross-sectional views.

As shown in FIG. 29A and FIG. 29B, a semiconductor layer 512M is formedon a surface portion of a semiconductor substrate 531. Subsequently, anelement isolation insulating layer 512I is formed on the upper surfaceof the semiconductor layer 512M. Subsequently, a gate 512G is formed onthe semiconductor layer 512M via a not-shown insulating layer.Subsequently, a source 512S and a drain 512D are formed on both sides ofthe gate 512G to form a transistor 532. Subsequently, an interlayerinsulating film 514 a is formed thereon, and an interlayer insulatingfilm 514 b is formed.

Subsequently, in the region that forms a non-hollow portion, trenchesand holes are formed in parts of the interlayer insulating films 514 aand 514 b. Subsequently, a conductive material is buried in the holes toform connection pillars 514 c to 514 e. In this case, the connectionpillar 514 c is electrically connected to the source 512S of atransistor 532, and the connection pillar 514 d is electricallyconnected to the drain 512D, for example. The connection pillar 514 e iselectrically connected to the source 512S of another transistor 532, forexample. Subsequently, a conductive material is buried in the trenchesto form interconnection units 514 f and 514 g. The interconnection unit514 f is electrically connected to the connection pillar 514 c and theconnection pillar 514 d. The interconnection unit 514 g is electricallyconnected to the connection pillar 514 e. Subsequently, an interlayerinsulating film 514 h is formed on the interlayer insulating film 514 b.

As shown in FIG. 30A and FIG. 30B, an interlayer insulating film 514 imade of silicon oxide (SiO₂) is formed on the interlayer insulating film514 h using the CVD (chemical vapor deposition) method, for example.Subsequently, holes are formed in prescribed positions of the interlayerinsulating film 514 i, a conductive material (for example, a metalmaterial) is buried, and the upper surface is planarized using the CMP(chemical mechanical polishing) method. Thereby, a connection pillar 514j connected to the interconnection unit 514 f and a connection pillar514 k connected to the interconnection unit 514 g are formed.

As shown in FIG. 31A and FIG. 31B, a recess is formed in a region of theinterlayer insulating film 514 i that forms a hollow portion 570, and asacrifice layer 514 l is buried in the recess. The sacrifice layer 514 lmay be formed using a material that can be formed into a film at lowtemperature, for example. The material that can be made into a film atlow temperature is silicon germanium (SiGe) or the like, for example.

As shown in FIG. 32A and FIG. 32B, an insulating film 561 bf that formsa film unit 564 (70 d) is formed on the interlayer insulating film 514 iand the sacrifice layer 514 l. The insulating film 561 bf may be formedusing silicon oxide (SiO₂) or the like, for example. A plurality ofholes are provided in the insulating film 561 bf, and a conductivematerial (for example, a metal material) is buried in the plurality ofholes to form a connection pillar 561 fa and a connection pillar 562 fa.The connection pillar 561 fa is electrically connected to the connectionpillar 514 k, and the connection pillar 562 fa is electrically connectedto the connection pillar 514 j.

As shown in FIG. 33A and FIG. 33B, a conductive layer 561 f that formsan interconnection 557 is formed on the insulating film 561 bf, theconnection pillar 561 fa, and the connection pillar 562 fa.

As shown in FIG. 34A and FIG. 34B, a stacked film 550 f is formed on theconductive layer 561 f.

As shown in FIG. 35A and FIG. 35B, the stacked film 550 f is processedinto a prescribed shape, and an insulating film 565 f that forms aninsulating layer 565 is formed thereon. The insulating film 565 f may beformed using silicon oxide (SiO₂) or the like, for example.

As shown in FIG. 36A and FIG. 36B, part of the insulating film 565 f isremoved, and the conductive layer 561 f is processed into a prescribedshape. Thereby, an interconnection 557 is formed. At this time, part ofthe conductive layer 561 f forms a connection pillar 562 fb electricallyconnected to the connection pillar 562 fa. Then, an insulating film 566f that forms an insulating layer 566 is formed thereon.

As shown in FIG. 37A and FIG. 37B, an opening 566 p is formed in theinsulating film 566 f. Thereby, the connection pillar 562 fb is exposed.

As shown in FIG. 38A and FIG. 38B, a conductive layer 562 f that formsan interconnection 558 is formed on the upper surface. Part of theconductive layer 562 f is electrically connected to the connectionpillar 562 fb.

As shown in FIG. 39A and FIG. 39B, the conductive layer 562 f isprocessed into a prescribed shape. Thereby, an interconnection 558 isformed. The interconnection 558 is electrically connected to theconnection pillar 562 fb.

As shown in FIG. 40A and FIG. 40B, an opening 5660 with a prescribedshape is formed in the insulating film 566 f. The insulating film 561 bfis processed via the opening 566 o, and the sacrifice layer 514 l isremoved via the opening 566 o. Thereby, a hollow portion 570 is formed.The removal of the sacrifice layer 514 l can be performed using the wetetching method, for example.

When a fixing unit 567 is shaped like a ring, the space between the edgeof the non-hollow portion above the hollow portion 570 and the film unit564 is filled with an insulating film, for example.

Thus, a pressure sensor is formed.

Fourth Embodiment

The embodiment relates to a microphone using the pressure sensoraccording to the embodiments described above.

FIG. 41 is a schematic cross-sectional view illustrating a microphoneaccording to a fourth embodiment.

A microphone 320 according to the embodiment includes a printed circuitboard 321, a cover 323, and a pressure sensor 310. The printed circuitboard 321 includes a circuit of an amplifier etc., for example. Anacoustic hole 325 is provided in the cover 323. Sound 329 passes throughthe acoustic hole 325 to enter the inside of the cover 323.

As the pressure sensor 310, any one of the pressure sensors described inregard to the embodiments and modifications thereof are used.

The microphone 320 reacts to sound pressure. By using a high-sensitivitypressure sensor 310, a high-sensitivity microphone 320 is obtained. Thepressure sensor 310 is mounted on the printed circuit board 321, and anelectric signal line is provided, for example. The cover 323 is providedon the printed circuit board 321 so as to cover the pressure sensor 310.

The embodiment can provide a high-sensitivity microphone.

Fifth Embodiment

The embodiment relates to a blood pressure sensor using the pressuresensor according to the embodiments described above.

FIG. 42A and FIG. 42B are schematic views illustrating a blood pressuresensor according to a fifth embodiment.

FIG. 42A is a schematic plan view illustrating the skin on an artery ofa person. FIG. 42B is a cross-sectional view taken along line H1-H2 ofFIG. 42A.

In the embodiment, the pressure sensor 310 is used as a blood pressuresensor 330. Any one of the pressure sensors described in regard to theembodiments and modifications thereof are used as the pressure sensor310.

Thus, high-sensitivity pressure sensing can be made by a small-sizedpressure sensor. By pressing the pressure sensor 310 against the skin333 on an artery 331, the blood pressure sensor 330 can make bloodpressure measurement continuously.

The embodiment can provide a high-sensitivity blood pressure sensor.

Sixth Embodiment

The embodiment relates to a touch panel using the pressure sensor of theembodiments described above.

FIG. 43 is a schematic diagram illustrating a touch panel according to asixth embodiment.

In the embodiment, the pressure sensor 310 is used as a touch panel 340.Any one of the pressure sensors described in regard to the embodimentsand modifications thereof are used as the pressure sensor 310. In thetouch panel 340, the pressure sensor 310 is mounted at least one of in adisplay and outside a display.

The touch panel 340 includes a plurality of first interconnections 346,a plurality of second interconnections 347, a plurality of pressuresensors 310, and a control unit 341, for example.

In this example, the plurality of first interconnections 346 are alignedalong the Y-axis direction. Each of the plurality of firstinterconnections 346 extends along the X-axis direction. The pluralityof second interconnections 347 are aligned along the X-axis direction.Each of the plurality of second interconnections 347 extends along theY-axis direction.

Each of the plurality of pressure sensors 310 is provided in theintersection portion of each of the plurality of first interconnections346 and each of the plurality of second interconnections 347. Onepressure sensor 310 forms one sensing element 310 e for detection. Here,the intersection portion includes the position where the firstinterconnection 346 and the second interconnection 347 cross each otherand a region around this.

One end 310 a of each of the plurality of pressure sensors 310 isconnected to each of the plurality of first interconnections 346. Theother end 310 b of each of the plurality of pressure sensors 310 isconnected to each of the plurality of second interconnections 347.

The control unit 341 is connected to the plurality of firstinterconnections 346 and the plurality of second interconnections 347.

The control unit 341 includes a circuit for the first interconnection346 d connected to the plurality of first interconnections 346, acircuit for the second interconnection 347 d connected to the pluralityof second interconnections 347, and a control circuit 345 connected tothe circuit for the first interconnection 346 d and the circuit for thesecond interconnection 347 d, for example.

The pressure sensor 310 can make high-sensitivity pressure sensing witha small size. Thus, a high-definition touch panel can be provided.

The pressure sensor according to the embodiment can be used for variouspressure sensor devices such as atmospheric pressure sensors and airpressure sensors for tires, as well as the uses mentioned above.

The embodiment can provide a strain sensing element, a pressure sensor,a microphone, a blood pressure sensor, and a touch panel of highsensitivity.

Hereinabove, embodiments of the invention are described with referenceto specific examples. However, the invention is not limited to thesespecific examples. For example, one skilled in the art may appropriatelyselect specific configurations of components of sensing elements,pressure sensors, microphones, blood pressure sensors, and touch panelssuch as film units, strain sensing elements, first magnetic layers,second magnetic layers, and intermediate layers from known art andsimilarly practice the invention. Such practice is included in the scopeof the invention to the extent that similar effects thereto areobtained.

Further, any two or more components of the specific examples may becombined within the extent of technical feasibility and are included inthe scope of the invention to the extent that the purport of theinvention is included.

Moreover, all strain sensing elements, pressure sensors, microphones,blood pressure sensors, and touch panels practicable by an appropriatedesign modification by one skilled in the art based on the strainsensing elements, the pressure sensors, microphones, the blood pressuresensors, and the touch panels described above as embodiments of theinvention also are within the scope of the invention to the extent thatthe spirit of the invention is included.

Various other variations and modifications can be conceived by thoseskilled in the art within the spirit of the invention, and it isunderstood that such variations and modifications are also encompassedwithin the scope of the invention.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the invention.

What is claimed is:
 1. A sensing element provided on a film beingdeformable, the sensing element comprising: a non-magnetic layer; afirst magnetic layer; a layer provided between the non-magnetic layerand the first magnetic layer, the layer contacting the non-magneticlayer, the layer including at least one selected from the groupconsisting of an oxide and a nitride; a second magnetic layer providedbetween the layer and the first magnetic layer; and a spacer layerprovided between the first magnetic layer and the second magnetic layer,wherein at least a part of the second magnetic layer is amorphous andincludes boron, an electric resistance of the sensing element isconfigured to change in accordance with a deformation of the film, thesecond magnetic layer includes a first portion and a second portion, thefirst portion is provided between the second portion and the spacerlayer, and a concentration of boron in the first portion is lower than aconcentration of boron in the second portion.
 2. The element accordingto claim 1, wherein the oxide includes an oxide of at least one selectedfrom the group consisting of magnesium, aluminum, silicon, titanium,vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc,zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver,hafnium, tantalum, tungsten, tin, cadmium, and gallium, and the nitrideincludes a nitride of at least one selected from the group consisting ofmagnesium, aluminum, silicon, titanium, vanadium, chromium, manganese,iron, cobalt, nickel, copper, zinc, zirconium, niobium, molybdenum,ruthenium, rhodium, palladium, silver, hafnium, tantalum, tungsten, tin,cadmium, and gallium.
 3. The element according to claim 1, wherein thelayer includes an oxide of at least one selected from the groupconsisting of magnesium, titanium, vanadium, zinc, tin, cadmium, andgallium.
 4. The element according to claim 1, wherein the layer includesmagnesium oxide.
 5. The element according to claim 1, wherein athickness of the layer is not more than one nanometer.
 6. The elementaccording to claim 1, wherein a concentration of boron included in thelayer is not less than 5 atomic percent and not more than 35 atomicpercent.
 7. The element according to claim 1, wherein the first portionhas crystallinity, and at least a part of the second portion isamorphous.
 8. The element according to claim 1, wherein amagnetostriction constant of the second magnetic layer is not less than1×10⁻⁵.
 9. The element according to claim 1, wherein a coercivity of thesecond magnetic layer is not more than 5 oersteds.
 10. The elementaccording to claim 1, wherein a sheet resistivity of the layer is lowerthan a sheet resistivity of the spacer layer.
 11. A sensing elementprovided on a film being deformable, the sensing element comprising: anon-magnetic layer; a first magnetic layer; a layer provided between thenon-magnetic layer and the first magnetic layer, the layer contactingthe non-magnetic layer, the layer including at least one elementselected from the group consisting of magnesium, silicon, and aluminum;a second magnetic layer provided between the layer and the firstmagnetic layer; and a spacer layer provided between the first magneticlayer and the second magnetic layer, wherein at least a part of thesecond magnetic layer is amorphous and includes boron, an electricresistance of the sensing element is configured to change in accordancewith a deformation of the film, the second magnetic layer includes afirst portion and a second portion, the first portion is providedbetween the second portion and the spacer layer, and a concentration ofboron in the first portion is lower than a concentration of boron in thesecond portion.
 12. A pressure sensor comprising: a film beingdeformable; and a sensing element provided on the film, the sensingelement including: a non-magnetic layer; a first magnetic layer; a layerprovided between the non-magnetic layer and the first magnetic layer,the layer contacting the non-magnetic layer, the layer including atleast one selected from the group consisting of an oxide and a nitride;a second magnetic layer provided between the layer and the firstmagnetic layer; and a spacer layer provided between the first magneticlayer and the second magnetic layer, wherein at least a part of thesecond magnetic layer is amorphous and includes boron, an electricresistance of the sensing element is configured to change in accordancewith a deformation of the film, the second magnetic layer includes afirst portion and a second portion, the first portion is providedbetween the second portion and the spacer layer, and a concentration ofboron in the first portion is lower than a concentration of boron in thesecond portion.
 13. A microphone comprising: a pressure sensor, thepressure sensor including: a film being deformable; and a sensingelement provided on the film, the sensing element including: anon-magnetic layer; a first magnetic layer; a layer provided between thenon-magnetic layer and the first magnetic layer, the layer contactingthe non-magnetic layer, the layer including at least one selected fromthe group consisting of an oxide and a nitride; a second magnetic layerprovided between the layer and the first magnetic layer; and a spacerlayer provided between the first magnetic layer and the second magneticlayer, wherein at least a part of the second magnetic layer is amorphousand includes boron, and an electric resistance of the sensing element isconfigured to change in accordance with a deformation of the film, thesecond magnetic layer includes a first portion and a second portion, thefirst portion is provided between the second portion and the spacerlayer, and a concentration of boron in the first portion is lower than aconcentration of boron in the second portion.
 14. A blood pressuresensor comprising: a pressure sensor, the pressure sensor including: afilm being deformable; and a sensing element provided on the film, thesensing element including: a non-magnetic layer; a first magnetic layer;a layer provided between the non-magnetic layer and the first magneticlayer, the layer contacting the non-magnetic layer, the layer includingat least one selected from the group consisting of an oxide and anitride; a second magnetic layer provided between the layer and thefirst magnetic layer; and a spacer layer provided between the firstmagnetic layer and the second magnetic layer, wherein at least a part ofthe second magnetic layer is amorphous and includes boron, and anelectric resistance of the sensing element is configured to change inaccordance with a deformation of the film, the second magnetic layerincludes a first portion and a second portion, the first portion isprovided between the second portion and the spacer layer, and aconcentration of boron in the first portion is lower than aconcentration of boron in the second portion.
 15. A touch panelcomprising: a pressure sensor, the pressure sensor including: a filmbeing deformable; and a sensing element provided on the film, thesensing element including: a non-magnetic layer; a first magnetic layer;a layer provided between the non-magnetic layer and the first magneticlayer, the layer contacting the non-magnetic layer, the layer includingat least one selected from the group consisting of an oxide and anitride; a second magnetic layer provided between the layer and thefirst magnetic layer; and a spacer layer provided between the firstmagnetic layer and the second magnetic layer, wherein at least a part ofthe second magnetic layer is amorphous and includes boron, and anelectric resistance of the sensing element is configured to change inaccordance with a deformation of the film, the second magnetic layerincludes a first portion and a second portion, the first portion isprovided between the second portion and the spacer layer, and aconcentration of boron in the first portion is lower than aconcentration of boron in the second portion.